Hydraulic system for working machine and control valve

ABSTRACT

A hydraulic system includes a first hydraulic device, a second hydraulic device, a first control valve to control the first hydraulic device, a second control valve disposed on a downstream side of the first control valve and configured to control the second hydraulic device, a communication tube connecting the first hydraulic device to the first control valve, a supply fluid tube connecting the first control valve to the second control valve, a connection fluid tube disposed on the first control valve, the connection fluid tube connecting the communication tube to the supply fluid tube, a discharge fluid tube connected to the first control valve, a setting portion disposed on the discharge fluid tube and configured to increase a pressure in the discharge fluid tube, a branching fluid tube branched from the connection fluid tube and connected to the discharge fluid tube, and a throttle disposed on the branching fluid tube.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part application ofco-pending U.S. patent application Ser. No. 15/978,729, filed May 14,2018, which claims priority to Japanese Patent Application Nos.JP2017-182585, filed Sep. 22, 2017 and JP2017-097651, filed May 16,2017. U.S. patent application Ser. No. 15/978,729; Japanese PatentApplication Nos. 2017-182585 and JP2017-097651 are hereby incorporatedby reference in their entireties as set forth in full herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a hydraulic system for a workingmachine and to a control valve.

Discussion of the Background

Japanese Unexamined Patent Application Publication No. 2010-270527discloses a hydraulic system for a working machine. The working machinedisclosed in Japanese Unexamined Patent Application Publication No.2010-270527 includes a boom, a bucket, a boom cylinder configured tooperate the boom, a bucket cylinder configured to operate the bucket, anauxiliary actuator configured to operate an auxiliary attachment, afirst control valve configured to control stretching and shortening ofthe boom cylinder, a second control valve configured to controlstretching and shortening of the bucket cylinder, and a third controlvalve configured to operate the auxiliary actuator.

SUMMARY OF THE INVENTION

A hydraulic system of a working machine includes a hydraulic pumpconfigured to output an operation fluid, a first hydraulic deviceconfigured to be operated by the operation fluid, a second hydraulicdevice other than the first hydraulic device, the second hydraulicdevice being configured to be operated by the operation fluid, a firstcontrol valve configured to control the first hydraulic device, a secondcontrol valve disposed on a downstream side of the first control valveand configured to control the second hydraulic device, a communicationtube connecting the first hydraulic device to the first control valve,the communication tube being configured to supply a return fluid thatreturns from the first hydraulic device to the first control valve, asupply fluid tube connecting the first control valve to the secondcontrol valve, the supply fluid tube being configured to supply thereturn fluid to the second control valve, a connection fluid tubedisposed on the first control valve, the connection fluid tubeconnecting the communication tube to the supply fluid tube, a dischargefluid tube connected to the first control valve, a setting portiondisposed on the discharge fluid tube and configured to increase apressure in the discharge fluid tube, a branching fluid tube branchedfrom the connection fluid tube, the branching fluid tube being connectedto the discharge fluid tube, and a throttle disposed on the branchingfluid tube.

A hydraulic system of a working machine includes a hydraulic pumpconfigured to output an operation fluid, a first hydraulic deviceconfigured to be operated by the operation fluid, a second hydraulicdevice other than the first hydraulic device, the second hydraulicdevice being configured to be operated by the operation fluid, a firstcontrol valve configured to control the first hydraulic device, a secondcontrol valve disposed on a downstream side of the first control valveand configured to control the second hydraulic device, a firstcommunication tube connecting the first hydraulic device to the firstcontrol valve, the first communication tube being configured to supply areturn fluid that returns from the first hydraulic device to the firstcontrol valve, a second communication tube other than the firstcommunication tube, the second communication tube connecting the firsthydraulic device to the first control valve and being configured tosupply the return fluid that returns from the first hydraulic device tothe first control valve, a supply fluid tube connecting the firstcontrol valve to the second control valve, the supply fluid tube beingconfigured to supply the return fluid to the second control valve, afirst connection fluid tube disposed on the first control valve, thefirst connection fluid tube connecting the first communication tube tothe supply fluid tube, a second connection fluid tube other than thefirst connection fluid tube, the second connection fluid tube beingdisposed on the first control valve and connecting the secondcommunication tube to the supply fluid tube, a discharge fluid tubeconnected to the first control valve, a first branching fluid tubebranched from the first connection fluid tube, the first branching fluidtube being connected to the discharge fluid tube, a second branchingfluid tube branched from the second connection fluid tube, the secondbranching fluid tube being connected to the discharge fluid tube, afirst throttle disposed on the first branching fluid tube, and a secondthrottle disposed on the second branching fluid tube, the secondthrottle being smaller than the first throttle.

A control valve includes a first port to which a first fluid tube isconnected, the first fluid tube being connected to a first hydraulicdevice, a second port to which a second fluid tube is connected, thesecond fluid tube being connected to the first hydraulic device, a thirdport to which a third fluid tube is connected, the third fluid tubebeing connected to a hydraulic pump configured to output an operationfluid, a fourth port to which a first discharge fluid tube is connected,the first discharge fluid tube being configured to discharge theoperation fluid, a fifth port configured to discharge the operationfluid to an outside, the operation fluid having passed through the firstport or the second port, a main body including a first inner fluid path,a second inner fluid path, a third inner fluid path, a fourth innerfluid path, and a fifth inner fluid path connected to the first port,the second port, the third port, the fourth port, and the fifth port,and a spool configured to move inside the main body to changecommunicating destinations of the first inner fluid path, the secondinner fluid path, the third inner fluid path, the fourth inner fluidpath, and the fifth inner fluid path and to move between a communicatingposition and a neutral position, the communicating position allowing thesecond inner fluid path and the fifth inner fluid path to becommunicated with each other or the first inner fluid path and the fifthinner fluid path to be communicated with each other, the spool includinga first communicating portion configured to allow the second inner fluidpath and the fourth inner fluid path to be communicated with each otheror the first inner fluid path and the fourth inner fluid path to becommunicated with each other when positioned between the communicatingposition and the neutral position.

A hydraulic system of a working machine includes a hydraulic pumpconfigured to output an operation fluid, a first hydraulic actuator, asecond hydraulic actuator, a first control valve including an input portinto which the operation fluid to be supplied to the first hydraulicactuator is introduced, the first control valve being configured tocontrol the first hydraulic actuator by the operation fluid to besupplied, a second control valve disposed on a downstream side of thefirst control valve and configured to control the second hydraulicactuator, a first fluid tube configured to connect the first controlvalve to the second control valve and to supply a return fluid to thesecond control valve, the return fluid returning from the firsthydraulic actuator to the first control valve, a second fluid tube otherthan the first fluid tube, the second fluid tube being configured toconnect the first control valve to the second control valve and to becommunicated with the first fluid tube, and a third fluid tubeconfigured to be communicated with the second fluid tube and to returnthe return fluid of the first fluid tube to the input port.

DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a view illustrating a hydraulic system (a hydraulic circuit)according to a first embodiment of the present invention;

FIG. 2 is a view illustrating a modified example of the hydraulic system(the hydraulic circuit) according to the first embodiment;

FIG. 3 is a view illustrating a hydraulic system (a hydraulic circuit)according to a second embodiment of the present invention;

FIG. 4A is a view illustrating an inside of a control valve being in aneutral position according to the second embodiment;

FIG. 4B is a view illustrating the inside of the control valve being ina position between the neutral position and a first position accordingto the second embodiment;

FIG. 4C is a view illustrating the inside of the control valve being inthe first position according to the second embodiment;

FIG. 5 is a view illustrating a hydraulic system (a hydraulic circuit)according to a third embodiment of the present invention;

FIG. 6 is a view illustrating a whole of a skid steer loader exemplifiedas a working machine according to the embodiments;

FIG. 7 is a view illustrating a modified example of the hydraulic system(the hydraulic circuit) of FIG. 5; and

FIG. 8 a view illustrating a modified example of the hydraulic system(the hydraulic circuit) of FIG. 5.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings. The drawings are tobe viewed in an orientation in which the reference numerals are viewedcorrectly.

First Embodiment

FIG. 6 shows a side view of a working machine 1 according to embodimentsof the present invention. FIG. 6 shows a skid steer loader as an exampleof the working machine 1. However, the working machine according to theembodiments of the present invention is not limited to the skid steerloader, but may be another kind of the loader working machine such as acompact track loader or the like. Further, the working machine may beanother working machine other than the loader work machine.

The working machine 1 includes a machine body (a vehicle body) 2, acabin 3, a working device 4, a traveling device 5A, and a travelingdevice 5B.

The cabin 3 is mounted on the machine body 2. An operator seat 8 isdisposed at a rear portion of an inside of the cabin 3. In explanationsof the embodiments of the present invention, a front side (a left sidein FIG. 6) of the operator seated on the operator seat 8 of the workingmachine 1 is referred to as the front (a front side), a rear side (aright side in FIG. 6) of the operator seated on the operator seat 8 ofthe working machine 1 is referred to as the rear (a rear side), a leftside (a front surface side in FIG. 6) of the operator seated on theoperator seat 8 of the working machine 1 is referred to as the left (aleft side), and a right side (a back surface side in FIG. 6) of theoperator seated on the operator seat 8 of the working machine 1 isreferred to as the right (a right side). In addition, a horizontaldirection corresponding to a direction perpendicular to thefront-to-rear direction will be referred to as a machine widthdirection. A direction extending from the center portion of the machinebody 2 to the right portion or the left portion will be referred to asmachine outward. In other words, the machine outward is a machine widthdirection that corresponds to a direction separating away from themachine body 2. In the explanation, a direction opposite to the machineoutward is referred to as a machine inward. In other words, the machineinward is a machine width direction that corresponds to a directionapproaching the machine body 2.

The cabin 3 is mounted on the machine body 2. The working device 4 is adevice configured to perform a work, and is mounted on the machine body2. The traveling device 5A is a device configured to allow the machinebody 2 to travel, and is disposed on the left side of the machine body2. The traveling device 5B is a device configured to allow the machinebody 2 to travel, and is disposed on the right side of the machine body2. A prime mover (a motor) 7 is disposed at a rear portion of an insideof the machine body 2. The prime mover 7 is a diesel engine (an engine).Meanwhile, it should be noted that the prime mover 7 is not limited tothe engine and may be an electric motor or the like.

On the left side of the operator seat 8, a traveling lever 9L isprovided. On the right side of the operator seat 8, a traveling lever 9Ris provided. The traveling lever 9L disposed on the left is provided foroperating the travel device 5A disposed on the left, and the travelinglever 9R disposed on the right is provided for operating the traveldevice 5B disposed on the right.

The working device 4 includes a boom 10, a bucket 11, a lift link 12, acontrol link 13, a boom cylinder (a hydraulic cylinder) 14 and a bucketcylinder 17. The boom 10 is provided on the side of the machine body 2.The bucket 11 is provided on a tip portion (a front end) of the boom 10.The lift link 12 and the control link 13 support a base portion (a rearportion) of the boom 10. The boom cylinder 14 moves the boom 10 upwardand downward.

More specifically, the lift link 12, the control link 13, and the boomcylinder 14 are provided on the side of the machine body 2. The upperportion of the lift link 12 is pivotally supported by the upper portionof the base portion of the boom 10. The lower portion of the lift link12 is pivotally supported on the side portion of the rear portion of themachine body 2. The control link 13 is disposed forward from the liftlink 12. One end of the control link 13 is pivotally supported by alower portion of the base portion of the boom 10, and the other end ispivotally supported by the machine body 2.

The boom cylinder 14 is constituted of a hydraulic cylinder configuredto move the boom 10 upward and downward. The upper portion of the boomcylinder 14 is pivotally supported by the front portion of the baseportion of the boom 10. The lower portion of the boom cylinder 14 ispivotally supported by the side portion of the rear portion of themachine body 2. When the boom cylinder 14 is stretched and shortened,the boom 10 is swung up and down by the lift link 12 and the controllink 13. The bucket cylinder 17 is constituted of a hydraulic cylinderconfigured to swing the bucket 11.

The bucket cylinder 17 couples the left portion of the bucket 11 and theboom disposed on the left to each other, and couples the right portionof the bucket 11 and the boom disposed on the right to each other.Meanwhile, it should be noted that, instead of the bucket 11, anauxiliary attachment such as a hydraulic crusher, a hydraulic breaker,an angle bloom, an auger, a pallet fork, a sweeper, a mower, a snowblower may be attached to the tip portion (the front portion) of theboom 10.

In the present embodiment, the traveling devices 5A and 5B respectivelyemploy wheeled traveling devices 5A and 5B each having a front wheel 5Fand a rear wheel 5R. Meanwhile, traveling devices 5A and 5B of a crawlertype (including a semi-crawler type) may be employed as the travelingdevices 5A and 5B.

Next, a working-system hydraulic circuit (a working-system hydraulicsystem) disposed in the skid steer loader 1 will be described below.

As shown in FIG. 1, the working-system hydraulic system is a systemconfigured to operate the boom 10, the bucket 11, the auxiliaryattachment, and the like. And, the working-system hydraulic systemincludes a control valve unit 70 and a hydraulic pump of working system(a first hydraulic pump) P1. In addition, the working-system hydraulicsystem includes a second hydraulic pump P2 different from the firsthydraulic pump P1.

The first hydraulic pump P1 is a pump configured to be operated by thepower of the prime mover 7, and is constituted of a gear pump ofconstant-displacement type (a constant-displacement type gear pump). Thefirst hydraulic pump P1 is configured to output an operation fluid (ahydraulic oil) stored in a tank (an operation fluid tank) 15. The secondhydraulic pump P2 is a pump configured to be operated by the power ofthe prime mover 7, and is constituted of a gear pump ofconstant-displacement type (a constant-displacement type gear pump). Thesecond hydraulic pump P2 is configured to output the operation fluidstored in the tank (the operation fluid tank) 15.

Meanwhile, in the hydraulic system, the second hydraulic pump P2 isconfigured to output the hydraulic fluid for signals (a signal hydraulicfluid) and the hydraulic fluid for control (a control hydraulic fluid).Each of the hydraulic fluid for signals (the signal hydraulic fluid) andthe hydraulic fluid for control (the control hydraulic fluid) isreferred to as a pilot fluid (a pilot oil).

The control valve unit 70 includes a plurality of control valves 20. Theplurality of control valves 20 are valves configured to controlhydraulic actuators (hydraulic devices) of various types, the hydraulicactuators being disposed on the working machine 1. The hydraulicactuator is a device configured to be operated by the hydraulic fluid,for example, a hydraulic cylinder, a hydraulic motor, and the like. Inthe embodiment, the plurality of control valves 20 include a firstcontrol valve 20A, a second control valve 20B, and a third control valve20C.

Firstly, the second control valve 20B and the third control valve 20Cwill be described below.

The second control valve 20B is a valve configured to control ahydraulic cylinder (a bucket cylinder) 17 that is configured to controlthe bucket 11. In other words, the second control valve 20B is a valveconfigured to control the bucket cylinder 17 that is a second hydraulicdevice configured to be operated by the hydraulic fluid. The thirdcontrol valve 20C is a valve configured to control the hydraulicactuators (the hydraulic cylinder, the hydraulic motor, and the like) 16mounted on the auxiliary attachment.

The second control valve 20B is a three-position switching valve havinga spool directly acting with a pilot fluid (referred to as a pilotdirect-acting spool type three-position switching valve). The secondcontrol valve 20B is configured to be switched to a neutral position 20b 3, to a first position 20 b 1 other than the neutral position 20 b 3,and to a second position 20 b 2 other than the neutral position 20 b 3and the first position 20 b 1. In the second control valve 20B, theswitching between the neutral position 20 b 3, the first position 20 b1, and the second position 20 b 2 is performed by a spool moved byoperation of the operation member. A bucket cylinder 17 is connected tothe second control valve 20B by a fluid tube.

Thus, when the second control valve 20B is set to the first position 20b 1 by the operation of the operating member, the bucket cylinder 17 isshortened. When the bucket cylinder 17 is shortened, the bucket 11performs a shoveling operation. When the second control valve 20B is setto the second position 20 b 2 by the operation of the operating member,the bucket cylinder 17 is stretched. When the bucket cylinder 17 isstretched, the bucket 11 performs a dumping operation.

Meanwhile, the switching of the second control valve 20B is performed bydirectly moving the spool with the operating member. However, the spoolmay be moved by the pressure of the operation fluid (the pilot fluid).The second control valve 20B is connected to the first control valve 20Aby a central fluid tube 68 a. The second control valve 20B and the thirdcontrol valve 20C are connected each other by a central fluid tube 68 b.When the second control valve 20B is in the neutral position 20B3, theoperation fluid supplied to the second control valve 20B is supplied tothe third control valve 20C through the central fluid tube 68 b.

The third control valve 20C is a three-position switching valve having aspool directly acting with a pilot fluid (referred to as a pilotdirect-acting spool type three-position switching valve). The thirdcontrol valve 20C is configured to be switched to a neutral position20C3, to a first position 20C1 other than the neutral position 20C3, andto a second position 20C2 other than the neutral position 20C3 and thefirst position 20C1. In the third control valve 20C, the switchingbetween the neutral position 20C3, the first position 20C1, and thesecond position 20C2 is performed by a spool moved by a pressure of thepilot fluid.

A connecting member 18 is connected to the third control valve 20Cthrough supply/discharge fluid tubes 83 a and 83 b. The supply/dischargefluid tubes 83 a and 83 b include a first fluid supply/discharge fluidtube 83 a and a second fluid supply/discharge fluid tube 83 b. A fluidtube connected to the hydraulic actuator 16 of the auxiliary attachmentis connected to the connecting member 18.

Thus, when the third control valve 20C is set to the first position20C1, the operation fluid can be supplied from the first fluidsupply/discharge fluid tube 83 a to the hydraulic actuator 16 of theauxiliary attachment. When the third control valve 20C is set to thesecond position 20C2, the operation fluid can be supplied from thesecond fluid supply/discharge fluid tube 83 b to the hydraulic actuator16 of the auxiliary attachment.

In this manner, when the operation fluid is supplied to the hydraulicactuator 16 from the supply/discharge fluid tube 83 a or thesupply/discharge fluid tube 83 b, the hydraulic actuator 16 (theauxiliary attachment) can be operated. Meanwhile, when the third controlvalve 20C is in the neutral position 20C3, the hydraulic fluid suppliedfrom the central fluid tube 68 b to the third control valve 20C isdischarged from the central fluid tube 68 c connected to the thirdcontrol valve 20C.

Next, the first control valve will be described below.

As shown in FIG. 1, the first control valve 20A is a valve configured tobe applied to a series circuit. In the series circuit having a controlvalve on the upstream side (for example, the first control valve 20A)and a control valve on the downstream side (for example, the secondcontrol valve 20B), the operation fluid (a return fluid) returning fromthe hydraulic actuator to the first control valve 20A in the operationof the first control valve 20A flows to the second control valve 20B.The first control valve 20A is a valve configured to output a part ofthe return fluid to a fluid tube configured to discharge the operationfluid, the return fluid returning from the hydraulic actuator in theoperation.

In the present embodiment, the first control valve 20A is connected byto a fluid tube a hydraulic cylinder (a boom cylinder) 14 that is one ofthe hydraulic actuators. In other words, the first control valve 20A isa valve configured to control the boom cylinder 14 that is the firsthydraulic device configured to be activated by the hydraulic fluid. Inaddition, the first control valve 20A discharges the hydraulic fluid toa fourth fluid tube (a discharge fluid tube) 24 described later, theoperation fluid returning from the boom cylinder 14.

The boom cylinder 14 includes a cylindrical body 14 a, a rod 14 bmovably provided on the cylindrical body 14 a, and a piston 14 cprovided on the rod 14 b. The boom cylinder 14 and the first controlvalve 20A are connected each other by communication tubes 21 and 22. Thecommunication tubes 21 and 22 have a first fluid tube (a firstcommunication tube) 21 and a second fluid tube (second communicationtube) 22.

In other words, the first fluid tube (the first communication tube) 21is a fluid tube in which the return fluid from the boom cylinder 14flows, the return fluid being outputted at the time of shortening of theboom cylinder 14 that is the first hydraulic device. In addition, thesecond fluid tube (the second communication tube) 22 is a fluid tube inwhich the return fluid from the boom cylinder 14 flows, the return fluidbeing outputted at the time of stretching of the boom cylinder 14 thatis the first hydraulic device. Each of the first fluid tube 21 and thesecond fluid tube 22 is configured to supply the operation fluid and isconstituted of a tubular member such as a hydraulic hose, a pipe, acoupler, and a joint.

A first supply/discharge port 14 d for supplying and discharging theoperation fluid is provided on a base end portion (on a side opposite tothe rod 14 b side) of the cylindrical body 14 a. A secondsupply/discharge port 14 e for supplying and discharging the operationfluid is provided on a tip end portion (on the rod 14 b side) of thecylindrical body 14 a. When the boom cylinder 14 is shortened, the boomcylinder 14 discharges the operation fluid from the firstsupply/discharge port 14 d. When the boom cylinder 14 is stretched, theboom cylinder 14 discharges the operation fluid from the secondsupply/discharge port 14 e.

One end of the first fluid tube 21 is connected to the firstsupply/discharge port 14 d, and one end of the second fluid tube 22 isconnected to the second supply/discharge port 14 e. That is, the secondfluid tube 22 is a fluid tube connected to the boom cylinder 14 at aposition different from the first fluid tube 21 that is connected to theboom cylinder 14.

As shown in FIG. 1, the first control valve 20A is a three-positionswitching valve having a spool directly acting with a pilot fluid(referred to as a pilot direct-acting spool type three-positionswitching valve). The first control valve 20A is configured to beswitched to a neutral position 20 a 3, to a first position 20 a 1 otherthan the neutral position 20 a 3, and to a second position 20 a 2 otherthan the neutral position 20 a 3 and the first position 20 a 1.

The first control valve 20A has a plurality of ports. As shown in FIG.1, the plurality of ports include a first port 31, a second port 32, athird port 33, a fourth port 34, and a fifth port 35.

The first port 31 is a port configured to be connected to the other endof the first fluid tube 21 that is connected to the boom cylinder 14.Thus, the operation fluid flowing from the first port 31 toward the boomcylinder 14 passes through the first fluid tube 21, and then enters thefirst supply/discharge port 14 d of the boom cylinder 14. In addition,the operation fluid flowing from the first supply/discharge port 14 dtoward the first control valve 20A passes through the first fluid tube21, and then enters the first port 31.

The second port 32 is a port configured to be connected to the other endof the second fluid tube 22 that is connected to the boom cylinder 14.Thus, the operation fluid flowing from the second port 32 toward theboom cylinder 14 passes through the second fluid tube 22, and thenenters the second supply/discharge port 14 e of the boom cylinder 14. Inaddition, the operation fluid flowing from the second supply/dischargeport 14 e toward the first control valve 20A passes through the secondfluid tube 22, and then enters the second port 32.

The third port 33 is a port configured to be connected to a third fluidtube (a main fluid tube) 23 that is connected to the first hydraulicpump P1 configured to discharge the operation fluid. In particular, thethird fluid tube 23 is branched into three tubes at the middle portionof the third fluid tube 23. And, a first branched fluid tube 23 a, asecond branched fluid tube 23 b, and a third branched fluid tube 23 care connected to the third port 33.

That is, the third port 33 includes a port 33 a connected to the firstbranched fluid tube 23 a, a port 33 b connected to the second branchedfluid tube 23 b, and a port 33 c connected to the third branched fluidtube 23 c.

The fourth port 34 is a port configured to be connected to a fourthfluid tube (a discharge fluid tube) 24 that is connected to theoperation fluid tank 15. In particular, the fourth fluid tube 24includes a fluid tube 24 a. The fluid tube 24 a is a fluid tubeconfigured to supply the operation fluid to the operation fluid tank 15,the operation fluid having passed through the first control valve 20A.

The discharge fluid tube 24 a includes a first discharge portion 24 a 1connected to the first fluid tube 21, a second discharge portion 24 a 2connected to the second fluid tube 22, a third discharge portion 24 a 3connecting the first discharge portion 24 a 1 and the second dischargeportion 24 a 2 to each other, and a fourth discharge portion 24 a 4connecting the third discharge portion 24 a 3 and the operation fluidtank 15 to each other.

Here, the fluid tube including the third discharge portion 24 a 3 andthe fourth discharge portion 24 a 4 may be respectively referred to asfirst discharge fluid tubes 24 a 3 and 24 a 4. In addition, thedischarge fluid tube 24 includes a second discharge fluid tube 24 b. Thesecond discharge fluid tube 24 b is a fluid tube branched from an outputfluid tube 68 and configured to supply, to the fluid tube 24 a, theoperation fluid having passed through the second control valve 20B andthe operation fluid having passed through the third control valve 20C.The second discharge fluid tube 24 b is a fluid tube connected to thefirst discharge fluid tube 24 a 3.

A relief valve 27 is connected to the first discharge portion 24 a 1,and another relief valve 27 is connected to the second discharge portion24 a 2. In addition, the first discharge portion 24 a 1 is provided witha bypass fluid tube, and the second discharge portion 24 a 2 is providedwith a bypass fluid tube, the bypass fluid tubes connecting both sidesof each of the relief valves 27 to each other. And, a check valve 29 isprovided in the bypass fluid tube. The check valve 29 is a valveconfigured to allow the operation fluid to flow from the discharge fluidtube 24 side to the communication tubes (the first communication tube 21and the second communication tube 22) and to block the operation fluidso as not to flow from the communication tubes to the discharge fluidtube 24 side.

The fourth discharge portion 24 a 4 is connected to the second dischargefluid tube 24 b. The third discharge portion 24 a 3 includes aconnecting portion 26 a and branched discharging portions 26 b and 26 c.The connecting portion 26 a connects the first discharging portion 24 a1 and the second discharging portion 24 a 2 to each other. The brancheddischarging portions 26 b and 26 c are branched from the connectingportion 26 a into at least two portions. The branched dischargingportions 26 b and 26 c are connected to the fourth port 34 of the firstcontrol valve 20A.

That is, the fourth port 34 includes a port 34 a and a port 34 b. Theport 34 a is connected to the branched discharge portion 26 b, and theport 34 b is connected to the branched discharge portion 26 c. In thepresent embodiment, the fourth port 34 is a port including two ports 34a and 34 b. However, the number of ports is not limited, and forexample, the number of ports may be one.

The fifth port 35 is a port configured to discharge, to the outside, theoperation fluid having passed through the first port 31 or the secondport 32. That is, the fifth port 35 is a port configured to discharge,to a control valve on the downstream side (the second control valve20B), the hydraulic fluid (the return fluid) returning from the boomcylinder 14 to the first port 31 or the hydraulic fluid (the returnedfluid) returning from the boom cylinder 14 to the second port 32.

Now, the working-system hydraulic system is provided with a fifth fluidtube 25. The fifth fluid tube 25 is a fluid tube configured to supplythe return fluid to the second control valve 20B when the first controlvalve 20A is in operation (when the spool 50 of the first control valve20A moves).

In particular, when the first control valve 20A is in the first position20 a 1, the first control valve 20A and the second control valve 20B areconnected to each other by a fifth fluid tube (a supply fluid tube) 25.The fifth fluid tube 25 allows the return fluid to pass through thefirst control valve 20A, the return fluid returning from the firsthydraulic actuator 14 to the first control valve 20A through the firstfluid tube 21, and then supplies the return fluid to the second controlvalve 20B.

One end of the fifth fluid tube 25 is branched into two portions, andthe first supply fluid tube 25 a (one of the two portions of thebranched fluid tube) and the second supply fluid tube 25 b (the otherone of the two portions of the branched fluid tube) are connected to thefifth port 35. That is, the fifth port 35 includes a port 35 a and aport 35 b. The port 35 is connected to the first supply fluid tube 25 a.And, the port 35 b is connected to the second supply fluid tube 25 b.

In the present embodiment, the fifth port 35 is a port including twoports 35 a and 35 b. However, the number of ports is not limited, andfor example, the number of ports may be one.

In addition, when the first control valve 20A is in the second position20 a 2, the first fluid tube 21 and the fifth fluid tube 25 areconnected to each other by the first connection fluid tube 61 a. Thefirst connection fluid tube 61 a is also referred to as a connectionfluid tube. The first connection fluid tube 61 a is a fluid tubedisposed on the first control valve 20A and is communicated with thefirst fluid tube 21.

In particular, the first connection fluid tube 61 a is a fluid tubeconfigured to connect the first port 31 of the first control valve 20Ato the fifth port 35 of the first control valve 20A when the firstcontrol valve 20A is set to the second position 20 a 2.

The working-system hydraulic system includes a branched fluid tube (afirst branched fluid tube) 65 a that is branched from the firstconnection fluid tube 61 a and configured to discharge the return fluid.The first branched fluid tube 65 a is a fluid tube branched from thefirst connection fluid tube 61 a and configured to be communicated withthe port 34 a when the first control valve 20A is in the second position20 a 2. A throttle portion (a first throttle portion) 67 a is disposedon the first branched fluid tube 65 a, the throttle portion beingconfigured to reduce a flow rate of the operation fluid.

The first throttle portion 67 a is constituted, for example, by makingone portion of the first branched fluid tube 65 a narrower than theother portions of the first branched fluid tube 65 a. In other words,the first throttle portion 67 a is constituted by reducing across-sectional area of the one portion to be smaller than the otherportion in the first branched fluid tube 65 a where the operation fluidflows. Meanwhile, the configuration of the first throttle portion 67 ais not limited to the example described above.

On the other hand, when the first control valve 20A is in the firstposition 20 a 1, the second fluid tube 22 and the fifth fluid tube 25are connected to each other by the second internal fluid tube (a secondconnection fluid tube) 61 b. The second connection fluid tube 61 b isalso referred to as a connection fluid tube. The second connection fluidtube 61 b is a fluid tube disposed on the first control valve 20A andcommunicated with the second fluid tube 22. The second connection fluidtube 61 b is a fluid tube configured to be connect the second port 32 ofthe first control valve 20A to the fifth port 35 of the first controlvalve 20A When the first control valve 20A is set to the first position20 a 1.

Meanwhile, the working-system hydraulic system has a branched fluid tube(a second branched fluid tube) 65 b that is branched off from the secondconnection fluid tube 61 b and configured to discharge the return fluid.In particular, the second branched fluid tube 65 b is a fluid tube thatis branched off from the second connection fluid tube 61 b and isconfigured to be communicated with the port 34 b when the first controlvalve 20A is in the first position 20 a 1. The second branched fluidtube 65 b is provided with a throttle portion (a second throttleportion) 67 b configured to reduce a flow rate of the operation fluid.

The second throttle portion 67 b is constituted, for example, by makingone portion of the second branched fluid tube 65 b narrower than theother portions of the second branched fluid tube 65 b. In other words,the second throttle portion 67 b is constituted by reducing across-sectional area of the one portion to be smaller than the otherportion in the second branched fluid tube 65 b where the operation fluidflows. Meanwhile, the configuration of the second throttle portion 67 bis not limited to the example described above.

In addition, the working-system hydraulic system has a setting portionconfigured to increase a pressure of the discharge fluid tube 24connected to the first branched fluid tube 65 a or to the secondbranched fluid tube 65 b.

As shown in FIG. 1, the setting portion includes a check valve (a firstcheck valve) 19 c and an oil cooler (a fluid cooler) 28, the check valve19 c being constituted of an operation valve. The check valve 19 c isprovided in the middle of the third discharge fluid tube 24 c that iscommunicated with the output fluid tube 68 (the central fluid tube 68 a,the central fluid tube 68 b, and the central fluid tube 68 c). The checkvalve 19 c is a valve configured to allow the hydraulic fluid to flowtoward the hydraulic fluid tank 22 and to prevents the hydraulic fluidfrom flowing toward the discharge fluid tube 68. The check valve 19 chas a setting member 19 c 1 configured to set a differential pressure.

The setting member 19 c 1 is constituted of a spring or the like, and isconfigured to generate a differential pressure by the valve body pushedwith a predetermined biasing force from a side opposite to a directionallowing the flow of the hydraulic fluid (from a direction preventingthe flow). The oil cooler 28 is provided in the middle of the firstdischarge fluid tubes 24 a 3 and 24 a 4 that are connected to the seconddischarge fluid tube 24 b. The hydraulic fluid discharged from the firstdischarge fluid tubes 24 a 3 and 24 a 4 flows into an inlet port 28 a ofthe oil cooler 28.

The discharge port 28 b, which is different from the inlet port 28 a ofthe oil cooler 28, is connected to the operation fluid tank 15. Here,paying attention to the second discharge fluid tube 24 b and the thirddischarge fluid tube 24 c provided with the check valve 19 c, the thirddischarge fluid tube 24 c and the second discharge fluid tube 24 b areconnected to each other by the connecting portion 26. The check valve 19c allows the hydraulic fluid to flow from the second discharge fluidtube 24 b toward the third discharge fluid tube 24 c, and blocks theoperation fluid flowing from the third discharge fluid tube 24 c to thesecond discharge fluid tube 24 b.

Thus, in the section between the check valve 19 c and the connectingsection 26 and in the section between the connecting section 26 and theinlet port 28 a of the oil cooler 28, the pressure of the hydraulicfluid is increased by the check valve 19 c serving as the settingportion. In this manner, when an amount of the operation fluid suppliedto the fifth fluid tube (a supply fluid tube) 25 decreases, for example,the operation fluid in the second discharge fluid tube 24 b and thefirst discharge fluid tubes 24 a 3 and 24 a 4 can be supplied to thefifth fluid tube 25 through the branched fluid tubes 65 a and 65 b andthe connection fluid tubes 61 a and 61 b.

For example, in the case where the boom cylinder 14 is stretched (theboom 10 is moved upward), the operation fluid (the return fluid) issupplied to the fifth fluid tube 25 through the second communicationtube 22, the second port 32, and the second connection fluid tube 61 b.

Here, in the case where the bucket cylinder 17 is stretched under thestate where the boom 10 is moved upward (the boom 11 is dumped), arelatively large amount of operation fluid is required. However, theoperation fluid in the second discharge fluid tube 24 b and in the firstdischarge fluid tubes 24 a 3 and 24 a 4 can be supplied to the fifthfluid tube 25 through the branched fluid tube 65 b and the connectionfluid tube 61 b. That is, it is possible to smoothly perform anoperation of dumping the bucket 11 with the boom 10 being moved upward.

FIG. 2 shows a modified example of the setting portion. As shown in FIG.2, the setting portion includes a throttle 67 d and a throttle 67 e, thethrottle 67 d being provided in the fourth discharge portion 24 a 4, thethrottle 67 e being provided in the third discharge fluid tube 24 c.

The hydraulic system of the working machine described above has thesetting portions (a throttle 67 d and a throttle 67 e) configured toincrease the pressures of the discharge fluid tubes (the brancheddischarge portions 26 b and 26 c of the first discharge fluid tube 24 a3) that are communicated with the branched fluid tubes (the firstbranched fluid tube 65 a and the second branched fluid tube 65 b)branched from the connection fluid tubes (the first connection fluidtube 61 a and the second connection fluid tube 61 b).

In this manner, the pressure in the section between the ports 34 a and34 b and the setting portion (the throttle 67 d and the throttle 67 e)can be increased in the branched discharge portions 26 b and 26 c. Thus,in the case where the operation fluid supplied to the fifth fluid tube(the supply fluid tube) 25 is for example reduced, it is possible tosupply the hydraulic fluid of the branched discharge portions 26 b and26 c to the fifth fluid tube through the branched fluid tubes 65 a and65 b and the connection fluid tubes 61 a and 61 b.

In the embodiment described above, the branched fluid tubes 65 a and 65b are provided respectively corresponding to the first position 20 a 1and the second position 20 a 2 of the first control valve 20A. However,It is also possible to provide the branched fluid tube 65 bcorresponding only to the first position 20 a 1 and to supply theoperation fluid of the discharge fluid tube 24 to the branched fluidtube 65 b.

In addition, it is preferred that the setting portion is configured toincrease a pressure in the discharge fluid tube 24, and the settingportion may be a relief valve provided in the fourth discharge portion24 a 4 and the third discharge fluid tube 24 c.

In addition, in the present embodiment, the discharge fluid tube 24 hastwo fluid tubes, that is, the second discharge fluid tube 24 b and thethird discharge fluid tube 24 c, However, when the second dischargefluid tube 24 b and the third discharge fluid tube 24 c are collectivelyconstituted of a single fluid tube, the setting portion may beconstituted of the oil cooler 28 and the check valve 19 c provided inthe middle portion of the fluid tube.

Meanwhile, the setting portion may be the oil cooler 28, the check valve19 c, a throttle, or a relief valve, or may be a combination thereof.

Meanwhile, a portion where the operation fluid flows of the secondthrottle portion 67 b has a cross-sectional area smaller than that ofthe first throttle portion 67 a. In other words, the second throttleportion 67 b through which the return fluid flows in the stretching ofthe boom cylinder 14 has a cross-sectional area smaller than that of thefirst throttle portion 67 a through which the return fluid flows whenthe boom cylinder 14 is shortened, at a portion through which the returnfluid flows.

That is, the second throttle portion 67 b has a better throttle effect,and the first diaphragm 67 a has a throttle effect less than that of thesecond diaphragm 67 b. Thus, the flow rate of the hydraulic fluidsupplied to the fifth fluid tube 25 under a condition where the firstcontrol valve 20A is set to the first position 20 a 1 can besubstantially equivalent to the flow rate of the operation fluidsupplied to the fifth fluid tube 25 under a condition where the firstcontrol valve 20A is set to the second position 20 a 2.

Orthogonal cross sections (the cross sections in a direction orthogonalto the rod 14) of the rod 14 b and the piston 14 c in the boom cylinder14 will be considered below. Regarding the orthogonal cross sections,the cross-sectional area of the piston 14 c is larger than thecross-sectional area of the rod 14 b. Thus, when the boom cylinder 14 isshortened, an amount of the operation fluid discharged from the firstsupply/discharge port 14 d is larger than an amount of the operationfluid discharged when the boom cylinder 14 is stretched.

That is, when the boom cylinder 14 is shortened, the amount of theoperation fluid returning to the first fluid tube 21 and the first port31 (the amount of the return fluid) will be large. Conventionally, sincethe return fluid is supplied directly to the second control valve 20B,the operability of the hydraulic actuator (the bucket cylinder 17)operated by the second control valve 20B is lowered when the secondcontrol valve 20B is operated simultaneously with the first controlvalve 20A.

That is, the operation feeling is different when the first control valve20A and the second control valve 20B are simultaneously operated fromwhen the operation is not performed simultaneously. On the other hand,according to the first control valve 20A, since the cross-sectional areaof the second throttle portion 67 b is smaller than the cross-sectionalarea of the first throttle portion 67 a, the operation feeling of thehydraulic actuator (the bucket cylinder 17) can be kept unchangedregardless of the stretching and shortening of the boom cylinder 14.

In particular, when the boom cylinder 14 is stretched (moving the boom10 upward), the operation fluid (the return fluid) discharged from thesecond supply/discharge port 14 e will be less than the operation fluid(the return fluid) discharged from the first supply/discharge port 14 ddue to the area ratio between the cross sections of the rod 14 b and thepiston 14 c of the cylinder 14 (the cross section in the directionorthogonal to the rod 14).

In addition, when the bucket cylinder 17 is stretched (the bucket 11 isdumped), an external force is applied in a direction to stretch thebucket cylinder 17 due to the loading on the bucket 11 or the like. Inthis manner, the pressure in the fifth fluid tube 25 will be lower thanthat in the connection portion 26 and that in the inlet port 28 a, andthus the fluid in the third discharge portion 24 a 3 flows to the secondbranched fluid tube 65 b without returning to the tank 15.

Note that a configuration similar to the configuration of the firstthrottle portion 67 a and the second throttle portion 67 b in thepresent embodiment can also be applied to the second control valve 20B.In that case, the throttle portion through which the return fluid flowswhen the bucket cylinder 17 is stretched has a cross-sectional areasmaller than that of the throttle portion through which the return fluidflows when the bucket cylinder 17 is shortened, in the portion throughwhich the return fluid flows.

Second Embodiment

FIG. 3 shows a second embodiment of the control valve 20 according tothe present invention. The control valve 20 of the second embodiment canbe applied to the control valve 20 of the first embodiment describedabove. Meanwhile, the explanation of the configurations similar to theconfigurations of the first embodiment will be omitted. As shown in FIG.3, the hydraulic system of the working machine is a system in which thefirst branched fluid tube 65 a, the second branched fluid tube 65 b, andthe setting portion (the operation valve) are not included.

As shown in FIG. 4A, the first control valve 20A includes a main bodyB1. The main body B1 is formed of a casting, a resin, or the like. Afluid tube through which the operation fluid flows is formed inside themain body B1. That is, the main body B1 has a first internal fluid tube41, a second internal fluid tube 42, a third internal fluid tube 43, afourth internal fluid tube 44, and a fifth internal fluid tube 45.

In convenience of the explanation, the left side of the page in FIG. 4Ato FIG. 4C is referred to as the left, the right side of the page isreferred to as the right, the directions toward the left and toward theright are referred to as a lateral direction, and a direction orthogonalto the lateral direction is referred to as a vertical direction. Inaddition, the first internal fluid tube 41, the second internal fluidtube 42, the third internal fluid tube 43, the fourth internal fluidtube 44, and the fifth internal fluid tube 45 will be explainedreferring to a cross-sectional view of FIG. 4A.

The first internal fluid tube 41 is a fluid tube formed inside the mainbody B1, and is communicated with the first port 31. A first port 31 isprovided on a left portion of the main body B1 in the lateral direction,and a first internal fluid tube 41 is formed next to the first port 31.The first internal fluid tube 41 is extended at least in thelongitudinal direction.

The second internal fluid tube 42 is a fluid tube formed inside the mainbody B1, and is communicated with the second port 32. The second port 32is provided on a right portion of the main body B1 in the lateraldirection, and a second internal fluid tube 42 is formed next to thesecond port 32. The second internal fluid tube 42 is extended at leastin the longitudinal direction.

The third internal fluid tube 43 is a fluid tube formed inside the mainbody B1, and is communicated with the third port 33. The third internalfluid tube 43 is formed in a central portion of the main body B1 in thelateral direction. In particular, the third internal fluid tube 43includes a left fluid tube 43 a, a right fluid tube 43 b, and a centralfluid tube 43 c.

The central fluid tube 43 c is formed at the center of the main body B1in the lateral direction, and is communicated with the port 33 c. Theleft fluid tube 43 a is located on the left of the central fluid tube 43c, and is communicated with the port 33 a. The right fluid tube 43 b islocated on the right of the central fluid tube 43 c, and is communicatedwith the port 33 b. The left fluid tube 43 a and the central fluid tube43 c are communicated with each other, and the right fluid tube 43 b andthe central fluid tube 43 c are communicated with each other. The leftfluid tube 43 a, the right fluid tube 43 b, and the central fluid tube43 c are extended at least in the vertical direction.

The fourth internal fluid tube 44 is a fluid tube formed inside the mainbody B1, and is communicated with the fourth port 34. In particular, thefourth internal fluid tube 44 includes a left fluid tube 44 a and aright fluid tube 44 b.

The left fluid tube 44 a is formed on the left portion of the main bodyB1 in the lateral direction, and is communicated with the port 34 a. Theleft fluid tube 44 a is located on the left of the first internal fluidtube 41. The right fluid tube 44 b is formed on the right portion of themain body B1 in the lateral direction, and is communicated with the port34 b. The right fluid tube 44 b is located on the right of the secondinternal fluid tube 42. The left fluid tube 44 a and the right fluidtube 44 b are extended at least in the vertical direction.

The fifth internal fluid tube 45 is a fluid tube formed inside the mainbody B1, and is communicated with the fifth port 35. In particular, thefifth internal fluid tube 45 includes a left fluid tube 45 a and a rightfluid tube 45 b.

The left fluid tube 45 a is formed on the left portion of the main bodyB1 in the lateral direction, and is communicated with the port 35 a. Theleft fluid tube 45 a is located between the first internal fluid tube 41and the left fluid tube 44 a of the fourth internal fluid tube 44. Theright fluid tube 45 b is formed on the right portion of the main body B1in the lateral direction, and is communicated with the port 35 b. Theright fluid tube 45 b is located between the second internal fluid tube42 and the right fluid tube 44 b of the fourth internal fluid tube 44.The left fluid tube 45 a and the right fluid tube 45 b are extended atleast in the vertical direction.

Meanwhile, a wall portion 36 (a through hole 36 a) having an annularshape extending from one end (the left end) of the main body B1 to theother end (the right end) in the lateral direction is formed. That is,the main body B1 is formed with the through hole 36 a extending straightinto which the spool 50 having a cylindrical shape is inserted.

The first internal fluid tube 41, the second internal fluid tube 42, thethird internal fluid tube 43, the fourth internal fluid tube 44, and thefifth internal fluid tube 45 extend to the annular wall portion 36constituting the through hole 36 a. The end portion 41 a of the firstinternal fluid tube 41 extends to the wall portion 36. The end portion42 a of the second internal fluid tube 42 extends to the wall portion36. The end portion 43 a 1 of the left fluid tube 43 a of the thirdinternal fluid tube 43 extends to the wall portion 36. The end portion43 b 1 of the right fluid tube 43 b of the third internal fluid tube 43extends to the wall portion 36. The end portion 43 c 1 of the centralfluid tube 43 c of the third internal fluid tube 43 extends to the wallportion 36.

The end portion 44 a 1 of the left fluid tube 44 a of the fourthinternal fluid tube 44 extends to the wall portion 36. The end portion44 b 1 of the right fluid tube 44 b of the fourth internal fluid tube 44extends to the wall portion 36. The end portion 45 a 1 of the left fluidtube 45 a of the fifth internal fluid tube 45 extends to the wallportion 36. The end portion 45 b 1 of the right fluid tube 45 b of thefifth internal fluid tube 45 extends to the wall portion 36.

In addition, each of the end portion 41 a, the end portion 42 a, the endportion 43 a 1, the end portion 43 b 1, the end portion 43 c 1, the endportion 44 a 1, the end portion 44 b 1, the end portion 45 a 1, and theend portion 45 b 1 is formed in a concave shape.

As shown in FIG. 4A, the first control valve 20A has a spool 50. Thespool 50 is configured to move inside the main body B1 to change thecommunication destinations of the first internal fluid tube 41, thesecond internal fluid tube 42, the third internal fluid tube 43, thefourth internal fluid tube 44 and the fifth internal fluid tube 45.

Hereinafter, the spool 50 will be described below in detail.

The spool 50 is formed to have a cylindrical shape. The spool 50 havinga cylindrical shape is inserted into the through hole 36 a formed insidethe main body B1. The left end or the right end of the spool 50protrudes from the main body B1. An operation member such as a lever isconnected to the protruding portion (the projecting portion) of thespool 50.

The spool 50 has a first communicating portion 51. The firstcommunicating portion 51 is a portion configured to communicate thesecond internal fluid tube 42, the fourth internal fluid tube 44, andthe fifth internal fluid tube 45 with each other. In particular, thefirst communicating portion 51 includes a first extending fluid tube 51a, the plurality of second extending fluid tubes 51 b, a plurality ofthird extending fluid tubes 51 c, and a first concaved portion 51 d.

The first extending fluid tube 51 a is a fluid tube extending inside thespool 50 in the longitudinal direction (an axial direction) of the spool50, and is formed by forming inside the spool 50 a hole extending in theaxial direction of the spool 50. The first extending fluid tube 51 aextends from the middle portion of the spool 50 to the right portion.The left end and the right end of the first extending fluid tube 51 aare closed. Accordingly, the hydraulic fluid that has entered the firstextending fluid tube 51 a flows inside the spool 50 in the axialdirection of the spool 50.

The plurality of second extending fluid tubes 51 b is a fluid tubeextending from the left end of the first extending fluid tube 51 a tothe outer circumference surface of the spool 50, and is communicatedwith the first extending fluid tube 51 a. The plurality of secondextending fluid tubes 51 b are communicated with the left portion of thefirst extending fluid tube 51 a. As shown in FIG. 4A, the spool 50 isprovided with the plurality of second extending fluid tubes 51 b at apredetermined interval in the circumferential direction.

The plurality of third extending fluid tubes 51 c are fluid tubesextending from the middle of the first extending fluid tube 51 a to theouter circumference face of the spool 50, and is communicated with thefirst extending fluid tube 51 a. The plurality of third extending fluidtubes 51 c are communicated with a middle portion of the first extendingfluid tube 51 a. As shown in FIG. 4A, the spool 50 is provided with theplurality of third extending fluid tubes 51 c at a predeterminedinterval in the circumferential direction.

The first concave portion 51 d is a portion formed by annularly dentingthe outer circumference surface of the spool 50. The first concaveportion 51 d is located on the right portion of the spool 50 and isoverlapped with the second extending fluid tube 51 b.

Meanwhile, the spool 50 has the second communicating portion 52.

The second communicating portion 52 is configured to communicate thefirst internal fluid tube 41 and the fifth internal fluid tube 45 witheach other. In addition, the second communicating portion 52 isconfigured to communicate the first internal fluid tube 41 and the thirdinternal fluid tube 43 with each other. In particular, the secondcommunicating portion 52 includes the second concave portion 52 a. Thesecond concave portion 52 a is a portion formed by annularly denting theouter circumference surface of the spool 50. The second recessed portion52 a is located on the left portion of the spool 50.

As shown in FIG. 4B, the spool 50 is positioned in the middle portion(the middle position 20 a 4) between the neutral position 20 a 3 and thefirst position 20 a 1. To be explained in detail, the first concaveportion 51 d and the end portion 42 a of the second internal fluid tube42 are overlapped (matched) with each other.

In addition, the third extending fluid tube 51 c is overlapped (matched)with the right fluid tube 44 b (the end portion 44 b 1) of the fourthinternal fluid tube 44. That is, when the first control valve 20A is inthe middle position 20 a 4, the second internal fluid tube 42 and thefourth internal fluid tube 44 can be communicated with each other.

When the first control valve 20A is in the middle position 20 a 4, thereturn fluid returning from the boom cylinder (the first hydraulicdevice) 14 to the first control valve 20A is discharged through thesecond fluid tube 22, the second internal fluid tube 42, the firstconcave portion 51 d, the first communicating portion 51, the fourthinternal fluid tube 44, and the fourth fluid tube 24, as indicated by R1in FIG. 4B.

As shown in FIG. 4C, the spool 50 is located at the first position 20 a1 (the communicating position 20 a 1). To be explained in detail, thefirst concave portion 51 d, the end portion 42 a of the second internalfluid tube 42, and the right fluid tube 45 b (the end portion 45 b 1) ofthe fifth internal fluid tube 45 are overlapped (matched) with eachother. In addition, the third extending fluid tube 51 c and the rightfluid tube 44 b (the end portion 44 b 1) of the fourth internal fluidtube 44 are overlapped (matched) with each other.

The second concave portion 52 a, the end portion 41 a of the firstinternal fluid tube 41, and the left fluid tube 43 a (the end portion 43a 1) of the third internal fluid tube 43 are overlapped (matched) witheach other. That is, when the first control valve 20A is in the firstposition 20 a 1, the second internal fluid tube 42, the fourth internalfluid tube 44, and the fifth internal fluid tube 45 can communicate witheach other.

When the first control valve 20A is in the first position 20 a 1, thereturn fluid returning from the boom cylinder 14 to the first controlvalve 20A is discharged through the second internal fluid tube 42, thefirst communicating portion 51, and the fourth internal fluid tube 44,as indicated by R2 in FIG. 4C. In addition, the return fluid returningfrom the boom cylinder 14 to the first control valve 20A is supplied tothe second control valve 20B through the second fluid tube 22, thesecond internal fluid tube 42, the first communicating portion 51, thefifth internal fluid tube 45, and the fifth fluid tube 25.

When the first control valve 20A is in the first position 20 a 1, thehydraulic fluid discharged from the operation fluid tank P1 is suppliedto the boom cylinder 14 through the third internal fluid tube 43 (theright fluid tube 43 a), the second internal fluid tube 42, the secondcommunicating portion 52, the first internal fluid tube 41 (the endportion 41 a), and the first fluid tube 21, as indicated by R3 in FIG.4C.

As described above, when the spool 50 is in the middle position 20 a 4,the spool 50 has the first communicating portion 51 configured tocommunicate the second internal fluid tube 42 and the fourth internalfluid tube 44 with each other. In this manner, in the case where thespool 50 is moved from the neutral position 20 a 3 to the first position20 a 1, the second internal fluid tube 42 and the fourth internal fluidtube 44 can be communicated with each other before the second internalfluid tube 42 and the fifth internal fluid tube 45 are communicated witheach other. In addition, in the case where the spool 50 is moved fromthe neutral position 20 a 3 to the first position 20 a 1, the secondinternal fluid tube 42 and the fourth internal fluid tube 44 can becommunicated with each other before the first internal fluid tube 41 andthe third internal fluid tube 43 are communicated with each other.

For example, when paying attention to the control valve (the firstcontrol valve 20A) on the upstream side and the control valve (thesecond control valve 20B) on the downstream side, the second internalfluid tube 42 and the fourth internal fluid tube 44 can be communicatedwith each other before the second internal fluid tube 42 and the fifthinternal fluid tube 45 are communicated with each other. Thus, theoperation fluid having passed through the control valve (the firstcontrol valve 20A) on the upstream side can be discharged independentlyfrom the control valve (the second control valve 20B) on the downstreamside, and thus it is possible to stably operate the first hydraulicequipment 14 disposed on the upstream side.

In addition, the spool 50 has a first communicating portion 51configured to communicate the second internal fluid tube 42, the fourthinternal fluid tube 44, and the fifth internal fluid tube 45 with eachother. The first communicating portion 51 includes a first extendingfluid tube 51 a, a plurality of second extending fluid tubes 51 b, and aplurality of third extending fluid tubes 51 c. The first extending fluidtube 51 a extends in the longitudinal direction of the spool 50. Theplurality of second extending fluid tubes 51 b extends from one end ofthe first extending fluid tube 51 a to the outer circumference surfaceof the spool 50. The plurality of third extending fluid tubes 51 cextends from a middle portion of the first extending fluid tube 51 a tothe outer circumference surface of the spool 50.

In this manner, the first communicating section 51 can be provided byforming the first extending fluid tube 51 a, the second extending fluidtube 51 b, and the third extending fluid tube 51 c in the inside of andon the outer circumference surface of the spool 50. Thus, the operationfluid can be discharged by the first communicating portion 51 withoutprocessing the main body B1, the first communicating portion 51 beingprovided in the spool 50.

Meanwhile, the configurations similar to the configurations of the firstcommunicating portion 51 can also be applied to the left portion of thespool 50. That is, when the configuration similar to the first position20 a 1 is applied to the second position 20 a 2, the first internalfluid tube 41 and the fourth internal fluid tube 44 are communicatedwith each other before the first internal fluid tube 41 and the fifthinternal fluid tube 45 are communicated with each other in the casewhere the spool 50 is moved from the neutral position 20 a 3 to thesecond position 20 a 2.

In addition, in the case where the spool 50 is moved from the neutralposition 20 a 3 to the second position 20 a 2, the first internal fluidtube 41 and the fourth internal fluid tube 44 can be communicated witheach other before the second internal fluid tube 42 and the thirdinternal fluid tube 43 are communicated with each other.

In the above description, the embodiment of the present invention hasbeen explained. However, all the features of the embodiments disclosedin this application should be considered just as examples, and theembodiments do not restrict the present invention accordingly. A scopeof the present invention is shown not in the above-described embodimentsbut in claims, and is intended to include all modifications within andequivalent to a scope of the claims.

In the above-described embodiment, the first hydraulic device is theboom cylinder 14, and the second hydraulic device is the bucket cylinder17. However, the first hydraulic device and the second hydraulic devicemay be other hydraulic cylinders and are not limited to theconfigurations. In addition, although the discharge fluid tube 24 isconnected to the operation fluid tank 15, the discharge destination ofthe operation fluid is not limited to the operation fluid tank 15, maybe a suction portion of the hydraulic pump, and may be anothercomponent, and is not limited to the configurations.

Third Embodiment

Referring to the drawings appropriately, preferred embodiments of thehydraulic system of the working machine according to the presentinvention and preferred embodiments of the working machine provided withthe hydraulic system will be described below.

Firstly, the working machine will be explained.

FIG. 6 shows a side view of the working machine according to theembodiment of the present invention. FIG. 6 shows a skid steer loader asan example of the working machine. However, the working machineaccording to the embodiment is not limited to the skid steer loader, andmay be another type of a loader working machine such as a compact trackloader. In addition, a working machine other than the loader workingmachine may be employed.

The working machine 1 includes the machine body (a vehicle body) 2, thecabin 3, the working device 4, and the traveling devices 5A and 5B.

The cabin 3 is mounted on the machine body 2. An operator seat 8 isdisposed at a rear portion of an inside of the cabin 3. In explanationsof the embodiments of the present invention, a front side (a left sidein FIG. 6) of the operator seated on the operator seat 8 of the workingmachine 1 is referred to as the front (a front side), a rear side (aright side in FIG. 6) of the operator seated on the operator seat 8 ofthe working machine 1 is referred to as the rear (a rear side), a leftside (a front surface side in FIG. 6) of the operator seated on theoperator seat 8 of the working machine 1 is referred to as the left (aleft side), and a right side (a back surface side in FIG. 6) of theoperator seated on the operator seat 8 of the working machine 1 isreferred to as the right (a right side).

In addition, a horizontal direction corresponding to a directionperpendicular to the front-to-rear direction will be referred to as amachine width direction. A direction extending from the center portionof the machine body 2 to the right portion or the left portion will bereferred to as machine outward. In other words, the machine outward is amachine width direction that corresponds to a direction separating awayfrom the machine body 2. In the explanation, a direction opposite to themachine outward is referred to as a machine inward. In other words, themachine inward is a machine width direction that corresponds to adirection approaching the machine body 2.

The cabin 3 is mounted on the machine body 2. The working device 4 is adevice configured to perform a work, and is mounted on the machine body2. The traveling device 5A is a device configured to allow the machinebody 2 to travel, and is disposed on the left side of the machine body2. The traveling device 5B is a device configured to allow the machinebody 2 to travel, and is disposed on the right side of the machine body2. A prime mover (a motor) 7 is disposed at a rear portion of an insideof the machine body 2. The prime mover 7 is a diesel engine (an engine).Meanwhile, it should be noted that the prime mover 7 is not limited tothe engine and may be an electric motor or the like.

On the left side of the operator seat 8, a traveling lever 9L isprovided. On the right side of the operator seat 8, a traveling lever 9Ris provided. The traveling lever 9L disposed on the left is provided foroperating the travel device 5A disposed on the left, and the travelinglever 9R disposed on the right is provided for operating the traveldevice 5B disposed on the right.

The working device 4 includes a boom 10, a bucket 11, a lift link 12, acontrol link 13, a boom cylinder (a hydraulic cylinder) 14 and a bucketcylinder 17. The boom 10 is provided on the side of the machine body 2.The bucket 11 is provided on a tip portion (a front end) of the boom 10.The lift link 12 and the control link 13 support a base portion (a rearportion) of the boom 10. The boom cylinder 14 moves the boom 10 upwardand downward.

More specifically, the lift link 12, the control link 13, and the boomcylinder 14 are provided on the side of the machine body 2. The upperportion of the lift link 12 is pivotally supported by the upper portionof the base portion of the boom 10. The lower portion of the lift link12 is pivotally supported on the side portion of the rear portion of themachine body 2. The control link 13 is disposed forward from the liftlink 12. One end of the control link 13 is pivotally supported by alower portion of the base portion of the boom 10, and the other end ispivotally supported by the machine body 2.

The boom cylinder 14 is constituted of a hydraulic cylinder configuredto move the boom 10 upward and downward. The upper portion of the boomcylinder 14 is pivotally supported by the front portion of the baseportion of the boom 10. The lower portion of the boom cylinder 14 ispivotally supported by the side portion of the rear portion of themachine body 2. When the boom cylinder 14 is stretched and shortened,the boom 10 is swung up and down by the lift link 12 and the controllink 13. The bucket cylinder 17 is constituted of a hydraulic cylinderconfigured to swing the bucket 11.

The bucket cylinder 17 couples the left portion of the bucket 11 and theboom disposed on the left to each other, and couples the right portionof the bucket 11 and the boom disposed on the right to each other.Meanwhile, it should be noted that, instead of the bucket 11, anauxiliary attachment such as a hydraulic crusher, a hydraulic breaker,an angle bloom, an auger, a pallet fork, a sweeper, a mower, a snowblower may be attached to the tip portion (the front portion) of theboom 10.

In the present embodiment, the traveling devices 5A and 5B respectivelyemploy wheeled traveling devices 5A and 5B each having a front wheel 5Fand a rear wheel 5R. Meanwhile, traveling devices 5A and 5B of a crawlertype (including a semi-crawler type) may be employed as the travelingdevices 5A and 5B.

Next, a working-system hydraulic circuit (a working-system hydraulicsystem) disposed in the skid steer loader 1 will be described below.

As shown in FIG. 5, the working-system hydraulic system is a systemconfigured to operate the boom 10, the bucket 11, the auxiliaryattachment, and the like. And, the working-system hydraulic systemincludes a control valve unit 70 and a hydraulic pump of working system(a first hydraulic pump) P1. In addition, the working-system hydraulicsystem includes a second hydraulic pump P2 different from the firsthydraulic pump P1.

The first hydraulic pump P1 is a pump configured to be operated by thepower of the prime mover 7, and is constituted of a gear pump ofconstant-displacement type (a constant-displacement type gear pump). Thefirst hydraulic pump P1 is configured to output an operation fluid (ahydraulic oil) stored in a tank (an operation fluid tank) 15. The secondhydraulic pump P2 is a pump configured to be operated by the power ofthe prime mover 7, and is constituted of a gear pump ofconstant-displacement type (a constant-displacement type gear pump).

The second hydraulic pump P2 is configured to output the operation fluidstored in the tank (the operation fluid tank) 15. Meanwhile, in thehydraulic system, the second hydraulic pump P2 is configured to outputthe hydraulic fluid for signals (a signal hydraulic fluid) and thehydraulic fluid for control (a control hydraulic fluid). Each of thehydraulic fluid for signals (the signal hydraulic fluid) and thehydraulic fluid for control (the control hydraulic fluid) is referred toas a pilot fluid (a pilot oil).

The plurality of control valves 20 are valves configured to controlvarious types of the hydraulic actuators disposed on the working machine1. The hydraulic actuator is a device configured to be operated by thehydraulic fluid, such as a hydraulic cylinder, a hydraulic motor, or thelike. In the embodiment, the plurality of control valves 20 include aboom control valve 20A, a bucket control valve 20B, and a auxiliarycontrol valve 20C.

The boom control valve 20A is a valve configured to control thehydraulic actuator (the boom cylinder) 14 that is configured to operatethe boom 10. The boom control valve 20A is a three-position switchingvalve having a spool directly acting with a pilot fluid (referred to asa pilot direct-acting spool type three-position switching valve). Theboom control valve 20A is configured to be switched to a neutralposition 20 a 3, to a first position 20 a 1 other than the neutralposition 20 a 3, and to a second position 20 a 2 other than the neutralposition 20 a 3 and the first position 20 a 1. In the boom control valve20A, the switching between the neutral position 20 a 3, the firstposition 20 a 1, and the second position 20 a 2 is performed by a spoolmoved by operation of the operation member.

The switching of the boom control valve 20A is performed by directlymoving the spool with manual operation of the operating member. However,the spool may be moved by the hydraulic operation (by the hydraulicoperation using a pilot valve, the hydraulic operation using aproportional valve), the spool may be moved by the electric operation(the electric operation by magnetizing the solenoid), or the spool maybe moved by other methods.

The boom control valve 20A and the first hydraulic pump P1 are connectedto each other by an output fluid tube 27. A discharge fluid tube 24 aconnected to the operation fluid tank 15 is connected to a section ofthe output fluid tube 27 between the boom control valve 20A and thefirst hydraulic pump P1. A relief valve (a main relief valve) 25 isdisposed on a middle portion of the discharge fluid tube 24 a.

The hydraulic fluid discharged from the first hydraulic pump P1 passesthrough the output fluid tube 27 and is supplied to the boom controlvalve 20A. In addition, the boom control valve 20A and the boom cylinder14 are connected to each other by a fluid tube 21.

In particular, the boom cylinder 14 includes a cylindrical body 14 a, arod 14 b movably provided on the cylindrical body 14 a, and a piston 14c provided on the rod 14 b. A first port 14 d for supplying anddischarging the operation fluid is provided on a base end portion (on aside opposite to the rod 14 b side) of the cylindrical body 14 a. Asecond port 14 e for supplying and discharging the operation fluid isprovided on a tip end (on the rod 14 b side) of the cylindrical body 14a.

The fluid tube 21 has a first connection fluid tube 21 a and a secondconnection fluid tube 21 b. The first connection fluid tube 21 aconnects the first port 31 of the boom control valve 20A to the firstport 14 d of the boom cylinder 14. The second connection fluid tube 21 bconnects the second port 32 of the boom control valve 20A to the secondport 14 e of the boom cylinder 14.

Thus, when the boom control valve 20A is set to the first position 20 a1, the operation fluid can be supplied from the first connection fluidtube 21 a to the first port 14 d of the boom cylinder 14, and theoperation fluid can be discharged from the second port 14 e of the boomcylinder 14 to the second connection fluid tube 21 b.

In this manner, the boom cylinder 14 is stretched, and thereby the boom10 moves upward. When the boom control valve 20A is set to the secondposition 20 a 2, it is possible to supply the operation fluid from thesecond connection fluid tube 21 b to the second port 14 e of the boomcylinder 14, and possible to discharge the operation fluid from thefirst port 14 d of the boom cylinder 14 to the first connection fluidtube 21 a. In this manner, the boom cylinder 14 is shortened, andthereby the boom 10 moves downward.

The bucket control valve 20B is a valve configured to control thehydraulic cylinder (the bucket cylinder) 17 that is configured tocontrol the bucket 11. The bucket control valve 20B is a three-positionswitching valve having a spool directly acting with a pilot fluid(referred to as a pilot direct-acting spool type three-positionswitching valve).

The bucket control valve 20B is configured to be switched to a neutralposition 20 b 3, to a first position 20 b 1 other than the neutralposition 20 b 3, and to a second position 20 b 2 other than the neutralposition 20 b 3 and the first position 20 b 1. In the second controlvalve 20B, the switching between the neutral position 20 b 3, the firstposition 20 b 1, and the second position 20 b 2 is performed by a spoolmoved by operation of the operation member.

The switching of the bucket control valve 20B is performed by directlymoving the spool with manual operation of the operating member. However,the spool may be moved by the hydraulic operation (by the hydraulicoperation using a pilot valve, the hydraulic operation using aproportional valve), the spool may be moved by the electric operation(the electric operation by magnetizing the solenoid), or the spool maybe moved by other methods.

The bucket control valve 20B and the bucket cylinder 17 are connected toeach other by a fluid tube 22. In particular, the bucket cylinder 17includes a cylindrical body 17 a, a rod 17 b movably provided on thecylindrical body 17 a, and a piston 17 c provided on the rod 17 b. Afirst port 17 d configured to supply and discharge the operation fluidis provided at the base end portion (on a side opposite to the rod 17 bside) of the cylindrical body 17 a. A second port 17 e configured tosupply and discharge the operation fluid is provided on the tip end side(on the rod 17 b) of the cylindrical body 17 a.

The fluid tube 22 has a first connection fluid tube 22 a and a secondconnection fluid tube 22 a. The first connection fluid tube 22 aconnects the first port 35 of the bucket control valve 20B to the secondport 17 e of the bucket cylinder 17. The second connection fluid tube 22a connects the second port 36 of the bucket control valve 20B to thefirst port 17 d of the bucket cylinder 17.

Thus, when the bucket control valve 20B is set to the first position20B1, the operation fluid can be supplied from the first connectionfluid tube 22 a to the second port 17 e of the bucket cylinder 17, andthe operation fluid can be discharged from the first port 17 d of thebucket cylinder 17 to the second supply tube 22 b.

In this manner, the bucket cylinder 17 is shortened, and thus the bucket11 is operated in a shoveling manner. When the bucket control valve 20Bis set to the second position 20 a 2, the hydraulic fluid can besupplied from the second supply tube 22 b to the first port 17 d of thebucket cylinder 17, and the hydraulic fluid can be discharged from thesecond port 17 e of the bucket cylinder 17 to the first connection fluidtube 22 a. In this manner, the bucket cylinder 17 is stretched, and thusthe bucket 11 is operated in the dumping manner.

Meanwhile, a discharge fluid tube 24 c is connected to the firstconnection fluid tube 22 a and the second connection fluid tube 22 b,and a relief valve 38 is provided on the discharge fluid tube 24 c. Aset pressure of the relief valve 38 is determined, for example, to behigher than a set pressure of the main relief valve 25.

The auxiliary control valve 20C is a three-position switching valvehaving a spool directly acting with a pilot fluid (referred to as apilot direct-acting spool type three-position switching valve). Theauxiliary control valve 20C is configured to be switched to a neutralposition 20 c 3, to a first position 20 c 1 other than the neutralposition 20 c 3, and to a second position 20 c 2 other than the neutralposition 20 c 3 and the first position 20 c 1.

In the auxiliary control valve 20C, the switching between the neutralposition 20 c 3, the first position 20 c 1, and the second position 20 c2 is performed by a spool moved by operation of the operation member. Aconnecting member 18 is connected to the auxiliary control valve 20C bythe supply/discharge fluid tubes 83 a and 83 b. A fluid tube connectedto the hydraulic actuator 16 of the auxiliary attachment is connected tothe connecting member 18.

Thus, when the auxiliary control valve 20C is set to the first position20 c 1, the operation fluid can be supplied from the supply/dischargefluid tube 83 a to the hydraulic actuator 16 of the auxiliaryattachment. When the auxiliary control valve 20C is set to the secondposition 20 c 2, the operation fluid can be supplied from thesupply/discharge fluid tube 83 b to the hydraulic actuator 16 of theauxiliary attachment.

In this manner, when the operation fluid is supplied from thesupply/discharge fluid tube 83 a or the supply/discharge fluid tube 83 bto the hydraulic actuator 16, the hydraulic actuator 16 (the auxiliaryattachment) can be operated.

Meanwhile, in the hydraulic system, a series circuit (a series fluidtube) is employed. In the series circuit, the hydraulic fluid havingreturned from the hydraulic actuator to the control valve on theupstream side can be supplied to the control valve disposed on thedownstream side. For example, paying attention to the bucket controlvalve 20B and the auxiliary control valve 20C, the bucket control valve20B is the control valve disposed on the upstream side, and theauxiliary control valve 20C is the control valve disposed on thedownstream side.

Hereinafter, the control valve on the upstream side is referred to as “afirst control valve”, and the control valve on the downstream side isreferred to as “a second control valve”. A control valve other than thefirst control valve and the second control valve, the control valvebeing provided on the upstream side of the second control valve isreferred to as “a third control valve”.

In addition, the hydraulic actuator corresponding to the first controlvalve is referred to as “a first hydraulic actuator”, the hydraulicactuator corresponding to the second control valve is referred to as “asecond hydraulic actuator”, and the hydraulic actuator corresponding tothe third control valve is referred to as “a third hydraulic actuator”.The fluid tube configured to supply the return fluid, which is theoperation fluid returning from the first hydraulic actuator to the firstcontrol valve, to the second control valve is referred to as “a firstfluid tube”.

In the embodiment, the bucket control valve 20B is referred to as “thefirst control valve”, the auxiliary control valve 20C is referred to as“the second control valve”, and the boom control valve 20A is referredto as “the third control valve”. In addition, the bucket cylinder 17 isreferred to as “the first hydraulic actuator”, the hydraulic actuator 16of the auxiliary attachment is referred to as “the second hydraulicactuator”, and the boom cylinder 14 is referred to as “the thirdhydraulic actuator”.

Hereinafter, the first control valve, the second control valve, and thethird control valve will be described below in detail.

The third control valve 20A and the output portion of the firsthydraulic pump P1 are connected to each other by an output fluid tube27. The output fluid tube 27 is branched off at a middle portion 47 a.The branched fluid tube of the output fluid tube 27 is connected to thefirst input port 46 a and the second input port 46 b of the thirdcontrol valve 20A. In addition, the output fluid tube 27 is connected tothe third input port 46 c of the third control valve 20A.

In this manner, the hydraulic fluid outputted from the first hydraulicpump P1 can be supplied into the third control valve 20A through theoutput fluid tube 27, the first input port 46 a, the second input port46 b, and the third input port 46 c. The third control valve 20A and thefirst control valve 20B are connected to each other by a central fluidtube 51. The central fluid tube 51 connects the third output port 41 cof the third control valve 20A to the third input port 42 c of the firstcontrol valve 20B.

Meanwhile, when the third control valve 20A is set to the neutralposition 20 a 3, the central fluid tube 53 c connecting the third inputport 46 c to the third output port 41 c is communicated through therein,and thereby the supplied fluid that is the operation fluid supplied fromthe output fluid tube 27 to the third control valve 20A passes throughthe third control valve 20A and then is supplied to the central fluidtube 51.

The third control valve 20A and the first control valve 20B areconnected to each other by a return fluid tube 61 separately from thecentral fluid tube 51. The return fluid tube 61 is a fluid tubeconfigured to supply the return fluid to the first control valve 20Bthrough the third control valve 20A, the return fluid returning from thethird hydraulic actuator 14 to the third control valve 20A. Forconvenience of the explanation, the return fluid tube 61 may be referredto as “a fourth fluid tube”.

The return fluid tube 61 has a second connection fluid tube 21 b, aninternal fluid tube 61 a, and an external fluid tube 61 b. The secondconnection fluid tube 21 b is a fluid tube connecting the second port 32of the third control valve 20A to the second port 14 e of the thirdhydraulic actuator 14, and also id a fluid tube in which the returnfluid discharged from the second port 14 e of the third hydraulicactuator 14 flows.

The second connection fluid tube 21 b is connected to the dischargefluid tube 24 b. The discharge fluid tube 24 b includes a fluid tube 24b 1, a fluid tube 24 b 2, and a fluid tube 24 b 3. The fluid tube 24 b 1is connected to the second connection fluid tube 21 b, the fluid tube 24b 2 is connected to the first discharge port 33 a and the seconddischarge port 33 b of the third control valve 20A, and the fluid tube24 b 3 connects the operation fluid tank 15 to a confluent portion ofthe fluid tube 24 b 1 and the passage 24 b 2. A relief valve 37 isprovided at the middle of the fluid tube 24 b 1. The set pressure of therelief valve 37 is set, for example, to be higher than the set pressureof the main relief valve 25.

The internal fluid tube 61 a is a fluid tube disposed on the thirdcontrol valve 20A and communicated with the second connection fluid tube21 b. In particular, when the third control valve 20A is set to thesecond position 20 a 2, the internal fluid tube 61 a is a fluid tubeconnecting the second port 32 of the third control valve 20A to thefirst output port 41 a of the third control valve 20A.

The external fluid tube 61 b is a fluid tube communicated with theinternal fluid tube 61 a and connected to the first control valve 20B.The external fluid tube 61 b connects the first output port 41 a of thethird control valve 20A to the first input port 42 a of the firstcontrol valve 20B, and connects the second output port 41 b of the thirdcontrol valve 20A to the second input port 42 b of the first controlvalve 20B. The middle portion of the external fluid tube 61 b isconnected to the central fluid tube 51.

In other words, the external fluid tube 61 b and the central fluid tube51 are connected to each other at a middle portion. In the externalfluid tube 61 b, a check valve 29 a is provided between a connectingportion 63 where the external fluid tube 61 b and the central fluid tube51 are connected to each other and the first control valve 20B. Thecheck valve 29 a allows the hydraulic fluid to flow from the connectingportion 63 to the first control valve 20B, and prevents the hydraulicfluid from flowing from the first control valve 20B to the connectingportion 63.

In addition, in the external fluid tube 61 b, a check valve 64 isprovided between the connecting portion 63 and the third control valve20A. The check valve 64 allows the hydraulic fluid to flow from thethird control valve 20A to the connecting portion 63, and prevents thehydraulic fluid from flowing from the connecting portion 63 to the thirdcontrol valve 20A.

The first control valve 20B and the second control valve 20C areconnected to each other by a central fluid tube (a second fluid tube)72. The central fluid tube 72 connects the third output port 43 c of thefirst control valve 20B to the third input port 44 c of the secondcontrol valve 20C.

Thus, when the first control valve 20B is set to the neutral position 20b 3, the supply fluid that is the operation fluid supplied to the firstcontrol valve 20B passes through a central fluid tube 73 c connectingthe third input port 42 c to the third output port 43 c, and then issupplied to the central fluid tube 72 connected to the third output port43 c.

The first control valve 20B and the second control valve 20C areconnected to each other by the first fluid tube 81 separately from thecentral fluid tube 72. The first fluid tube 81 is a fluid tubeconfigured to supply the return fluid to the second control valve 20Cthrough the first control valve 20B, the return fluid returning from thefirst hydraulic actuator 17 to the first control valve 20B.

The first fluid tube 81 has a fluid tube (a first connection fluid tube)22 a, an internal fluid tube 81 a, and an external fluid tube 81 b. Thefirst connection fluid tube 22 a is a fluid tube connecting the firstport 35 of the first control valve 20B to the second port 17 e of thefirst hydraulic actuator 17, and is a fluid tube in which the returnfluid discharged from the second port 17 e flows.

Meanwhile, the fluid tube (the second connection fluid tube) 22 b isconnected to the discharge fluid tube 24 b. The discharge fluid tube 24b has a fluid tube 24 b 4, a fluid tube 24 b 5, and a fluid tube 24 b 3.The fluid tube 24 b 4 is connected to the second connection fluid tube22 b, the fluid tube 24 b 5 is connected to the first discharge port 34a and the second discharge port 34 b of the first control valve 20B, andthe fluid tube 24 b 3 connects the operation fluid tank 15 to theconnecting portion of the fluid tube 24 b 4 and the fluid tube 24 b 5.

The internal fluid tube 81 a is a fluid tube provided on the firstcontrol valve 20B and communicated with the first connection fluid tube22 a. In particular, when the first control valve 20B is set to thesecond position 20 b 2, the internal fluid tube 81 a is a fluid tubeconnecting the second port 36 of the first control valve 20B to thefirst output port 43 a of the first control valve 20B.

The external fluid tube 81 b is a fluid tube communicated with theinternal fluid tube 81 a and connected to the second control valve 20C.The external fluid tube 81 b connects the first output port 43 a of thefirst control valve 20B to the first input port 44 a of the secondcontrol valve 20C, and connects the second output port 43 b of the firstcontrol valve 20B to the second output port 43 b of the first controlvalve 20B. The middle portion of the external fluid tube 81 b isconnected to the central fluid tube 73 c.

In other words, the external fluid tube 81 b and the central fluid tube73 c are connected to each other at a middle portion. In the externalfluid tube 81 b, a check valve 29 b is provided between a connectingportion 93 where the external fluid tube 81 b and the central fluid tube73 c are connected to each other and the second control valve 20C. Thecheck valve 29 b allows the hydraulic fluid to flow from the connectingportion 93 to the second control valve 20C, and prevents the hydraulicfluid from flowing from the second control valve 20C to the connectingportion 93.

In addition, in the external fluid tube 81 b, a check valve 94 isprovided between the connecting portion 93 and the first control valve20B. The check valve 94 allows the hydraulic fluid to flow from thefirst control valve 20B to the connecting portion 93, and prevents thehydraulic fluid from flowing from the connecting portion 93 to the firstcontrol valve 20B.

As described above, when the first control valve 20B is set to thesecond position 20B2 that is the side position, the supply fluid issupplied to the second input port 42 b, and the supply fluid passesthrough the second connection fluid tube 22 b and then is supplied tothe first hydraulic actuator 17.

On the other hand, when the first control valve 20B is set to the secondposition 20 b 2, the return fluid discharged from the second port 17 eof the first hydraulic actuator 17 passes through the first fluid tube81, that is, through the first connection fluid tube 22 a, the internalfluid tube 81 a, and the external fluid tube 81 b, and flows toward thesecond control valve 20C.

Meanwhile, the hydraulic system of the working machine is provided witha third fluid tube 90. The third fluid tube 90 is a fluid tubeconfigured to return the return fluid to the first control valve 20Bagain through the first fluid tube 81, the return fluid flowing from thefirst control valve 20B to the second control valve 20C.

In particular, the third fluid tube 90 is a fluid tube configured toreturn the return fluid to the input port of the first control valve 20B(the first input port 42 a and the second input port 42 b), the returnfluid being discharged from the first output port 43 a of the firstcontrol valve 20B and flowing through the external fluid tube 81 b.

For example, when the first control valve 20B is in the second position20 b 2, which is one of the side positions, the third fluid tube 90 is afluid tube connecting the third output port 43 c of the first controlvalve 20B to the third input port 42 c of the first control valve 20B.

In other words, in the case where the first control valve 20B is in thesecond position 20 b 2, the third fluid tube 90 and the second fluidtube 72 are connected to each other. It is preferred that the thirdfluid tube 90 is provided with a throttle portion 91 configured toreduce the flow rate of the operation fluid.

As described above, when the first control valve 20B is set to thesecond position 20 b 2 that is the side position, the supply fluid issupplied to the second input port 42 b, and the supply fluid passesthrough the second connection fluid tube 22 b and is supplied to thefirst hydraulic actuator 17.

On the other hand, when the first control valve 20B is set to the secondposition 20 b 2, the return fluid discharged from the second port 17 eof the first hydraulic actuator 17 passes through the internal fluidtube 81 a and the external fluid tube 81 b, and flows toward the secondcontrol valve 20C.

Consider the following case where the return fluid passes through thefirst fluid tube 81, the auxiliary control valve 20C is switched to thefirst position 20 c 1 or to the second position 20 c 2, and thereby thehydraulic actuator 16 fails to be operated due to an external force, thehydraulic actuator 16 fails to be operated when the hydraulic actuator16 constituted of a hydraulic cylinder reaches an end portion (an end)of the hydraulic cylinder, the supplying of the operation fluid isstopped, or the like under a condition where the hydraulic actuator 16of the auxiliary attachment is in operation.

In other words, a case will be considered where the return fluid passesthrough the first fluid tube 81 and no hydraulic fluid is introducedinto the first input port 44 a and the second input port 44 b of theauxiliary control valve 20C.

Under such states, since the return fluid in the first fluid tube 81 hasno way to flow in the case where the third fluid tube 90 is not providedto the first control valve 20B, a pressure on the bottom side of thefirst hydraulic actuator 17 communicated with the first fluid tube 81 isincreased. When the pressure on the bottom side of the first hydraulicactuator 17 is increased, a pressure on the rod side of the firsthydraulic actuator 17 is also increased.

When the cross sectional areas on the bottom side and on the rod sideare compared with each other inside the first hydraulic actuator 17, thesectional area on the bottom side is larger than the cross sectionalarea on the rod side. As the result, when the first hydraulic actuator17 is stretched due to the pressure increasing on the bottom side of thefirst hydraulic actuator 17, the pressure increasing on the rod sidewill be relatively large.

For example, when the above-described situation occurs in the case wherethe first hydraulic actuator 17 and the third hydraulic actuator 14 areoperated in combination, the operation of the first hydraulic actuator17 may be delayed.

On the other hand, when the operation fluid is not introduced into thefirst input port 44 a and the second input port 44 b of the auxiliarycontrol valve 20C in the case where the third fluid tube 90 is employed,the return fluid in the first fluid tube 81 flows to the second fluidtube 72 through the connecting portion 93. The return fluid flowing tothe second fluid tube 72 returns to the input port (the first input port42 a and the second input port 42 b) through the connecting portion 63.

In this manner, the return fluid in the first fluid tube 81 returns tothe first control valve 20B again through the second fluid tube 72 andthe third fluid tube 90, and thus the first hydraulic actuator 17 can beoperated smoothly.

That is, since the return fluid on the rod side of the first hydraulicactuator 17 can be returned to the bottom side of the first hydraulicactuator 17, a speed of the stretching of the first hydraulic actuator17 can be improved.

In particular, in a case where the first hydraulic actuator (the bucketcylinder) 17 and the third hydraulic actuator (the boom cylinder) 14 areoperated in combination, for example, in a case where the boom cylinder17 is stretched and the bucket cylinder 14 is stretched (in the casewhere the bucket cylinder 14 is operated in the dumping manner withmoving the boom 14 upward), the dumping of the bucket 11 can beperformed quickly.

As shown in FIG. 5, the hydraulic system of the working machine may beprovided with a discharge fluid tube 70 branched off from the internalfluid tube 61 c. The internal fluid tube 61 c is a fluid tube configuredto connect the first port 31 to the second output port 41 b when thethird control valve 20A is in the first position 20 a 1. The dischargefluid tube 70 is a fluid tube configured to be communicated with thefirst discharge port 33 a in the case where the first control valve 20Ais in the first position 20 a 1.

The discharge fluid tube 70 is provided with a throttle portion 71configured to reduce the flow rate of the operation fluid. The throttleportion 71 is constituted, for example, by making a part of thedischarge fluid tube 70 narrower than the other portions of thedischarge fluid tube 70. In other words, the throttle portion 71constituted by making the cross-sectional area of a portion throughwhich the operation fluid flows smaller than the other portions in thedischarge fluid tube 70.

Thus, since a part of the return fluid is discharged by the dischargefluid tube 70, the third hydraulic actuator 14 can be smoothly operated.Meanwhile, the configuration of the throttle portion 71 is not limitedto the example described above.

In the above description, the embodiment of the present invention hasbeen explained. However, all the features of the embodiments disclosedin this application should be considered just as examples, and theembodiments do not restrict the present invention accordingly. A scopeof the present invention is shown not in the above-described embodimentsbut in claims, and is intended to include all modifications within andequivalent to a scope of the claims.

In the embodiment described above, the operation fluid is discharged tothe operation fluid tank, but the operation fluid may be discharged toother components. That is, the fluid tube configured to discharge thehydraulic fluid may be connected to a portion other than the operationfluid tank, for example, the fluid tube may be connected to a suctionportion of the hydraulic pump (a portion configured to suck theoperation fluid), and the fluid tube may be connected to other portions.

In the embodiment described above, the control valve is a three-positionswitch valve. However, the number of switching positions is not limited,and the control valve may be constituted of a two-position switch valve,a four-position switch valve, or other switch valves. In the embodimentdescribed above, the hydraulic pump is constituted of aconstant-displacement pump. However, the hydraulic pump may beconstituted of a variable displacement pump configured to move a swashplate to change a discharge amount, or may be constituted of anotherhydraulic pump, for example.

In addition, the first hydraulic actuator, the second hydraulicactuator, the third hydraulic actuator, the first control valve, thesecond control valve, and the third control valve are not limited to theexamples of the embodiments described above, and it is only required tobe provided in the working machine 1.

In addition, a pressure increasing portion 130 may be added to thehydraulic system for the working machine of FIG. 5. FIG. 7 is ahydraulic system in which the pressure increasing portion 130 is addedto the hydraulic system for the working machine of FIG. 5.

The pressure increasing portion 130 is a portion configured to increasea pressure of the first fluid tube 81. In other words, the pressureincreasing portion 130 increases the pressure of the fluid tube (acenter fluid tube 75, the center fluid tube 72, the fluid tube 24 b 3,and the fluid tube 24 b 7) connected to the first fluid tube 81, andthereby increases the pressure of the first fluid tube 81.

The center fluid tube 75 is an fluid tube connected to the secondcontrol valve 20C and communicated with the center fluid tube 72. Thecenter fluid tube 75 and the fluid tube 24 b 3 are confluent with eachother at a confluent portion 76. The fluid tube 24 b 7 connects theconfluent portion 76, the hydraulic fluid tank 15, and the like to eachother.

The pressure increasing portion 130 includes the check valve 19 c, anoil cooler 28, and the like. Meanwhile, the pressure increasing portion130 may be constituted of anything as long as it increases the pressureof the discharge fluid tube 24 b, and may be constituted of a reliefvalve, a throttle portion (a throttle valve), or a choke valve.

In particular, the check valve 19 c is connected to an intermediateportion of the fluid tube 24 b 7 of the discharge fluid tube 24 b. Thecheck valve 19 c is a valve configured to allow the hydraulic fluid toflow toward the hydraulic fluid tank 15 and to prevent the hydraulicfluid from flowing toward the center fluid tube 75. The check valve 19 chas a setting member 19 c 1 configured to set a differential pressure.

The setting member 19 c 1 is constituted of a spring or the like. Thesetting member 19 c 1 pushes the valve body with a predetermined pushingforce from a side opposed to the direction permitting the flow of thehydraulic fluid (a blocking direction), and thereby generates thedifferential pressure. According to the check valve 19 c, it is possibleto increase the pressure of the hydraulic fluid on the upstream side ofthe fluid tube 24 b 7 from the inlet side of the check valve 19 c to theconfluent portion 76.

Thus, in the case where the first control valve 20B is set to the secondposition 20 b 2, the pressures of the hydraulic fluids in the centerfluid tube 75 and the center fluid tube 72 can be increased by the checkvalve 19 c. In this manner, the entire pressure of the first fluid tube81 connected to the center fluid tube 72 through the confluent portion93 can be increased.

That is, since the pressure of the first fluid tube 81 through which thereturn fluid flows can be increased, it is possible to facilitate thereturn fluid applied to the center fluid tube 72 through the confluentportion 93 to easily flow into the third fluid tube 90.

The oil cooler 28 is provided in the middle portion of the dischargefluid tube 24 b. The operation fluid discharged from the discharge fluidtube 24 b 3 flows into the inlet port 28 a of the oil cooler 28. Thedischarge port 28 b, which is different from the inlet port 28 a of theoil cooler 28, is connected to the hydraulic fluid tank 15.

Thus, in the case where the first control valve 20B is set to the secondposition 20 b 2, the pressures of the hydraulic fluids in the centerfluid tube 75 and the center fluid tube 72 can be increased also in thecase of the oil cooler 28 as in the case of the check valve 19 c.

As the result, the return fluid applied to the center fluid tube 72through the confluent portion 93 is facilitated to easily flow into thethird fluid tube 90. The return fluid that has passed through the thirdfluid tube 90 passes through the third input port 42 c, passes throughthe confluent portion 63, and then is introduced into the first inputport 42 a and the second input port 42 b.

FIG. 8 shows a modified example of the hydraulic system of the workingmachine shown in FIG. 5. In the modified example, the boom control valve20A is the “first control valve”, the bucket control valve 20B is the“second control valve”, and the auxiliary control valve 20C is the“third control valve”. In addition, the boom cylinder 14 is the “firsthydraulic actuator”, the bucket cylinder 17 is the “second hydraulicactuator”, and the hydraulic actuator 16 of the auxiliary attachment isthe “third hydraulic actuator”.

In addition, in the modified example, the first fluid tube is the returnfluid tube 61. That is, in the case of the modified example, the returnfluid (a first fluid tube) 61 has a second connection fluid tube 21 b,an inner fluid tube 61 c, and an outer fluid tube 61 b. The second fluidtube is the center fluid tube 51. The third fluid tube is the fluid tube190.

The fluid tube (a third fluid tube) 190 is a fluid tube through whichthe return fluid is returned to the first control valve 20A again, thereturn fluid passing through the return fluid tube (a first fluid tube)61 and flowing from the first control valve 20A to the second controlvalve 20B. In particular, the fluid tube 190 is a fluid tube throughwhich the return fluid is returned to an input port (a first input port46 a) of the first control valve 20A, the return fluid being dischargedfrom the second output port 41 b of the first control valve 20A andflowing through the external fluid tube 61 b.

For example, in the case where the first control valve 20A is in thefirst position 20 a 1 which is one of the lateral positions, the fluidtube 190 connects the third output port 41 c of the first control valve20A to the third input port 41 c of the first control valve 20A.

the third control valve 20<3input port 46c.

In other words, in the case where the first control valve 20A is in thefirst position 20 a 1, the fluid tube 190 and the center fluid tube (asecond fluid tube) 51 are connected to each other. It is preferred thatthe fluid tube 190 is provided with the throttle portion 191 forreducing the flow rate of the operation fluid.

According to the above description, in the case where the first controlvalve 20A is set to the first position 20 a 1 which is the lateralposition, the supply fluid is supplied to the first input port 46 a, andthe supply fluid passes through the first connection fluid tube 21 a,and then is supplied to the first hydraulic actuator 14.

In addition, in the case where the first control valve 20A is set to thefirst position 20 a 1, the return fluid discharged from the second port14 e of the first hydraulic actuator 14 passes through the return fluidtube (a first fluid tube) 61, that is, the second connection fluid tube21 b, the internal fluid tube 61 c, and the external fluid tube 61 b,and flows toward the second control valve 20B.

After passing through the confluent portion 63, the return fluid flowinginto the external fluid tube 61 b flows into the center fluid tube (asecond fluid tube) 51 and is introduced into the third input port 41 c.The return fluid introduced into the third input port 41 c flows to thefluid tube (a third fluid tube) 190, and returns to the input port (thefirst input port 46 a). The return fluid returning to the input port(the first input port 46 a) is introduced to the first input port 46 aand the second input port 46 b through the discharge fluid tube 27.

In this manner, the return fluid in the return fluid tube (a first fluidtube) 61 returns to the first control valve 20A again through the centerfluid tube (a second fluid tube) 51 and the fluid tube (a third fluidtube) 190, and thus the first hydraulic actuator 14 can be operatedsmoothly.

In addition, in the hydraulic system the hydraulic circuit) includingthe pressure increasing portion 130, the third fluid tubes 90 and 190may be provided to the control valve arranged on the most downstreamside of the plurality of control valves 20 as described above.

What is claimed is:
 1. A hydraulic system of a working machine comprising: a hydraulic pump to output an operation fluid; a first hydraulic device to be operated by the operation fluid; a second hydraulic device other than the first hydraulic device, the second hydraulic device being configured to be operated by the operation fluid; a first control valve to control the first hydraulic device; a second control valve disposed on a downstream side of the first control valve and configured to control the second hydraulic device; a communication tube connecting the first hydraulic device to the first control valve, the communication tube being configured to supply a return fluid that returns from the first hydraulic device to the first control valve; a supply fluid tube connecting the first control valve to the second control valve, the supply fluid tube being configured to supply the return fluid to the second control valve; a connection fluid tube disposed on the first control valve, the connection fluid tube connecting the communication tube to the supply fluid tube; a discharge fluid tube connected to the first control valve; a setting portion disposed on the discharge fluid tube and configured to increase a pressure in the discharge fluid tube; a branching fluid tube branched from the connection fluid tube, the branching fluid tube being connected to the discharge fluid tube; and a throttle disposed on the branching fluid tube.
 2. The hydraulic system according to claim 1, wherein the first hydraulic device is a hydraulic cylinder configured to be stretched and shortened, wherein the communication tube includes: a first communication tube in which the return fluid flows in the shortening of the first hydraulic device; and a second communication tube in which the return fluid flows in the stretching of the first hydraulic device, wherein the connection fluid tube is connected to the second communication tube and supplies the return fluid that is discharged from the second communication tube, and wherein the supply fluid tube is connected to the connection fluid tube and supplies the return fluid to the second control valve, the return fluid being discharged from the connection fluid tube.
 3. The hydraulic system according to claim 1, comprising an output fluid tube to supply the operation fluid outputted by the hydraulic pump to the first control valve and the second control valve, the output fluid tube including: a first output fluid tube connected to the first control valve; a second output fluid tube connected to the output fluid tube and connected to the first output control valve; and a third output fluid tube connected to the output fluid tube.
 4. The hydraulic system according to claim 3, wherein the setting portion includes an operation valve disposed on the third discharge fluid tube and configured to increase a pressure in the third discharge fluid tube.
 5. The hydraulic system according to claim 4, wherein the operation valve is a first check valve configured to allow the operation fluid to flow from the second discharge fluid tube to the third discharge fluid tube and to block the operation fluid not to flow from the third discharge fluid tube to the second discharge fluid tube.
 6. The hydraulic system according to claim 4, wherein the setting portion includes a cooler to cool the operation fluid discharged from the first discharge fluid tube.
 7. The hydraulic system according to claim 3, wherein the setting portion is disposed in the discharge fluid tube, the setting portion including any one of a cooler, a check valve, a throttle, and a relief valve.
 8. The hydraulic system according to claim 3, wherein the setting portion is a throttle disposed in the discharge fluid tube.
 9. A hydraulic system of a working machine comprising: a hydraulic pump to output an operation fluid; a first hydraulic device to be operated by the operation fluid; a second hydraulic device other than the first hydraulic device, the second hydraulic device being configured to be operated by the operation fluid; a first control valve to control the first hydraulic device; a second control valve disposed on a downstream side of the first control valve and configured to control the second hydraulic device; a first communication tube connecting the first hydraulic device to the first control valve, the first communication tube being configured to supply a return fluid that returns from the first hydraulic device to the first control valve; a second communication tube other than the first communication tube, the second communication tube connecting the first hydraulic device to the first control valve and being configured to supply the return fluid that returns from the first hydraulic device to the first control valve; a supply fluid tube connecting the first control valve to the second control valve, the supply fluid tube being configured to supply the return fluid to the second control valve; a first connection fluid tube disposed on the first control valve, the first connection fluid tube connecting the first communication tube to the supply fluid tube; a second connection fluid tube other than the first connection fluid tube, the second connection fluid tube being disposed on the first control valve and connecting the second communication tube to the supply fluid tube; a discharge fluid tube connected to the first control valve; a first branching fluid tube branched from the first connection fluid tube, the first branching fluid tube being connected to the discharge fluid tube; a second branching fluid tube branched from the second connection fluid tube, the second branching fluid tube being connected to the discharge fluid tube; a first throttle disposed on the first branching fluid tube; and a second throttle disposed on the second branching fluid tube, the second throttle being smaller than the first throttle.
 10. The hydraulic system according to claim 9, wherein the first hydraulic device is hydraulic cylinder configured to be stretched and shortened, to discharge the return fluid to the first communication tube in the shortening of the first hydraulic device, and to discharge the return fluid to the second communication tube in the stretching of the first hydraulic device, wherein the first connection fluid tube is connected to the first communication tube and supplies the return fluid that is discharged from the first communication tube, wherein the supply fluid tube is connected to the first connection fluid tube and supplies the return fluid to the second control valve, the return fluid being discharged from the first connection fluid tube, wherein the second connection fluid tube is connected to the second communication tube and supplies the return fluid that is discharged from the second communication tube, and wherein the supply fluid tube is connected to the second connection fluid tube and supplies the return fluid to the second control valve, the return fluid being discharged from the second connection fluid tube.
 11. The hydraulic system according to claim 9, comprising a second check valve disposed in the discharge fluid tube, the second check valve being configured to allow the operation fluid discharged from the first control valve to flow and to block the operation fluid not to flow toward the first control valve.
 12. A control valve comprising: a first port to which a first fluid tube is connected, the first fluid tube being connected to a first hydraulic device; a second port to which a second fluid tube is connected, the second fluid tube being connected to the first hydraulic device; a third port to which a third fluid tube is connected, the third fluid tube being connected to a hydraulic pump configured to output an operation fluid; a fourth port to which a first discharge fluid tube is connected, the first discharge fluid tube being configured to discharge the operation fluid; a fifth port to discharge the operation fluid to an outside, the operation fluid having passed through the first port or the second port; a main body including a first inner fluid path, a second inner fluid path, a third inner fluid path, a fourth inner fluid path, and a fifth inner fluid path connected to the first port, the second port, the third port, the fourth port, and the fifth port; and a spool to move inside the main body to change communicating destinations of the first inner fluid path, the second inner fluid path, the third inner fluid path, the fourth inner fluid path, and the fifth inner fluid path and to move between a communicating position and a neutral position, the communicating position allowing the second inner fluid path and the fifth inner fluid path to be communicated with each other or the first inner fluid path and the fifth inner fluid path to be communicated with each other, the spool including a first communicating portion to allow the second inner fluid path and the fourth inner fluid path to be communicated with each other or the first inner fluid path and the fourth inner fluid path to be communicated with each other when positioned between the communicating position and the neutral position.
 13. The control valve according to claim 12, wherein the spool is configured to allow the second inner fluid path and the fifth inner fluid path to be communicated with each other when the first inner fluid path and the third inner fluid path are communicated with each other.
 14. The control valve according to claim 12, wherein the first communicating portion includes a first extension fluid path extending in a longitudinal direction of the spool; a plurality of second extension fluid paths extending from one end of the first extension fluid path toward an outer circumference surface of the spool; and a plurality of third extension fluid paths extending from an intermediate portion of the first extension fluid path toward the outer circumference surface of the spool.
 15. The control valve according to claim 12, wherein the spool includes a second communicating portion to allow the first inner fluid path and the third inner fluid path to be communicated with each other, the second communicating portion being constituted of a concave portion formed on the outer circumference surface of the spool.
 16. A hydraulic system of a working machine comprising: a hydraulic pump to output an operation fluid; a first hydraulic actuator; a second hydraulic actuator; a first control valve including an input port into which the operation fluid to be supplied to the first hydraulic actuator is introduced, the first control valve being configured to control the first hydraulic actuator by the operation fluid to be supplied; a second control valve disposed on a downstream side of the first control valve and configured to control the second hydraulic actuator; a first fluid tube to connect the first control valve to the second control valve and to supply a return fluid to the second control valve, the return fluid returning from the first hydraulic actuator to the first control valve; a second fluid tube other than the first fluid tube, the second fluid tube being configured to connect the first control valve to the second control valve and to be communicated with the first fluid tube; and a third fluid tube to be communicated with the second fluid tube and to return the return fluid of the first fluid tube to the input port.
 17. The hydraulic system according to claim 16, wherein the first control valve is configured to be switched between a neutral position allowing a supplied fluid to pass through the first control valve and to be supplied to the second fluid tube, the supplied fluid being the operation fluid supplied to the first control valve, and a side position allowing the supplied fluid to be supplied to the first hydraulic actuator, allowing the return fluid to be supplied to the first fluid tube, and allowing the third fluid tube and the second fluid tube to be connected to each other.
 18. The hydraulic system according to claim 17, wherein the first hydraulic actuator is a hydraulic cylinder configured to be stretched and shortened, and is configured to discharge the operation fluid serving as the return fluid in the shortening and stretching of the first hydraulic actuator, wherein the first control valve includes a first output port and a second output port connected to the first fluid tube; and a third output port connected to the second fluid tube, and wherein the third fluid tube is configured to connect the input port to the third output port when the first control valve has the side position.
 19. The hydraulic system according to claim 18, wherein the first hydraulic actuator includes: a first port to discharge the operation fluid serving as the return fluid in the shortening of the first hydraulic actuator; and a second port to discharge the operation fluid serving as the return fluid in the stretching of the first hydraulic actuator, and wherein the first fluid tube includes: a fluid tube connecting the first control valve to the second port of the first hydraulic actuator, the fluid tube being configured to supply the return fluid discharged from the second port; a first internal fluid tube disposed on the first control valve and communicated with the fluid tube and the first output port; and an external fluid tube communicated with the first internal fluid tube and the second port and connected to the second control valve.
 20. The hydraulic system according to claim 16, comprising: a third hydraulic actuator; a third control valve to control the third hydraulic actuator; a fourth fluid tube connecting the first control valve to the third control valve, the fourth fluid tube being configured to supply the operation fluid to the first control valve, the operation valve serving as the return fluid returning from the third hydraulic actuator to the third control valve; and a discharge fluid tube to discharge the operation fluid serving as the return fluid returning from the third hydraulic actuator to the third control valve.
 21. The hydraulic system according to claim 16, comprising a bucket arranged on the boom, wherein the first hydraulic actuator is a boom cylinder to move the boom, and wherein the second hydraulic actuator is a boom cylinder to move the bucket.
 22. The hydraulic system according to claim 16, comprising a pressure increasing portion to increase a pressure of the operation fluid in the first fluid tube. 